The answer is that none save Allah can remove harm,
“If Allah touches you with harm, none can remove it but Him. If He touches you with good, He has power over all things” [Surah al-An’am (6): 17]
Sins are a cause for the onset of harm and asking for forgiveness removes its causes,
“Allah would never punish them while you were among them. Allah would not punish them as long as they sought forgiveness” [Surah al-Anfal (8): 33]
So He, Exalted is He, informed us that He would not punish the penitent. It is mentioned in a hadith,
Whoever frequently asks for forgiveness, Allah would appoint for him relief from every worry, a way out from every difficulty and provision coming from unimagined sources.
Allah, Exalted is He, says,
“Any disaster that strikes you is through what your own hands have earned and He pardons much” [Surah ash-Shura (42): 30]
His saying, “l have been amongst the wrong-doers” is an acknowledgment of his sin and also a request for forgiveness because this acknowledgment implicitly includes this request within it.
His saying, 'none has the right to be worshipped save You' affirms Tawhid al-Ilahiyyah. Good can only be procured by the will of Allah, everything He wills, is, and everything He does not will, is not. The obstacle to this good on the part of the servant is his sins, anything else that is outside the ability of the servant occurs by the decree of Allah This even though the actions of the servant occur by the decree of Allah, Exalted is He, Allah has appointed the observance of the legislated and the leaving of the prohibited to be the means to felicity and success.
Therefore the testification to tawhid opens the door to good and asking for forgiveness closes the door to evil.
This is why it is desirable to only attach ones hope to Allah and not to fear oppression and wrong-doing from Him for Allah does not oppress the servant in the slightest, instead it is they who oppress themselves. He should, however, fear that Allah recompense him for his sins and this is why (Ali (radiyAllahu ‘anhu) said, 'The servant should not put his hope in any save his Lord and not fear anything save his sins.' The Prophet (sallAllahu ‘alaihi wa sallam) entered upon a sick person and asked,
'In what state does this sickness find you?' he replied, 'I hope in Allah and fear my sins.' He (sallAllahu ‘alaihi wa sallam) said, 'These two never come together in the heart of a servant on such occasions except that Allah grants him what he hopes and saves him from what he fears.’ 
Hence hope should be placed in Allah and not any object of creation, not the ability or strength of a person or his actions. To put hope in other than Allah is a form of shirk, this applies even though Allah has set up means and causes (asbab) that lead to the procurement of good, but these means cannot exist independently, rather their must exist something that supports and aids them to achieve the goal, just as any obstacle hindering this achievement must be absent; hence it cannot be achieved and it cannot endure except by the will of Allah, Exalted is He. 
This is why it is said that to place ones reliance and hope in the means is to commit shirk, to deny the existence of the means is a sign of stupidity, and to turn away from them altogether is to impute the Divine Law with deficiency. This is why Allah, Exalted is He, says,
“So when you have finished, work on, and to your Lord direct your longing and attention!” [Surah ash-Sharh (94): 7-8]
Thereby ordering us to place our fervent desire in Him alone. He also says,
“Put your trust in Allah if you are believers” [Surah al-Ma'idah (5): 23]
The heart does not place its reliance except in one from whom it hopes for something. Therefore whoever places hope in his strength, ability, actions, friend, relative, teacher etc., not considering Allah, has placed a form of reliance upon that cause. Whoever places his hope in an object of creation will ultimately be disappointed for he is committing shirk,
“...As for anyone who associates others with Allah, it is as though he had fallen from the sky and the birds had seized him and carried him away, or the wind had dropped him in a distant place” [Surah al-Hajj (22): 31]
Similarly the polytheist fears objects of creation and places his hope in them and therefore lives in a state of dread as Allah, Exalted is He, says,
“We will cast terror into the hearts of the disbelievers because they have associated others with Allah for which He has not sent down any authority” [Al- Imran (3): 151]
To be free of shirk is to be in safety as Allah, Exalted is He, says,
“Those who have faith and do not mix up their faith with any wrong-doing, they are the ones who are safe; it is they who are guide” [Surah al-An’am (6): 82]
The Prophet (sallAllahu ‘alaihi wa sallam) explained wrong-doing in this verse to mean shirk, it is recorded in the Sabah on the authority of ibn Mas’ud,
When this verse was revealed it bore down heavily on the Companions of the Prophet (sallAllahu ‘alaihi wa sallam) and they said, 'Who amongst us has not committed wrong?' The Prophet (sallAllahu ‘alaihi wa sallam) said, "This refers to shirk, have you not heard the saying of the righteous servant,”
“Associating others with Allah is a terrible wrong” [Surah Luqman (31): 13]
Allah, Exalted is He, says,
“Some people set up equals with Allah, loving them as they should love Allah. But those who have faith have greater love for Allah. If only you could see those who do wrong at the time when they see the punishment, and that truly all strength belongs to Allah, and that Allah is severe in punishment. When those who were followed disown those who followed them, and they see the punishment, and the connection between them is severed; those who followed will say, `If only we could have another chance, we would disown them as they have disowned us.' In this way Allah will show them their actions as a cause of anguish and remorse for them. They will never leave the Fire” [Surah al-Baqarah (2): 165-167]
“Say: 'Call on those you make claims for apart from Him. They possess no power to remove any harm from you or to change anything.' Those they call on are themselves seeking the means by which they might approach their Lord - [striving as to] which of them would be closest to Him - and are hoping for His mercy and fearing His punishment. The punishment of your Lord is truly something to be feared” [Surah al-Isra’ (17): 56-57]
This is why Allah has mentioned the causes and ordered us not to depend upon them and instead to place our hope in Him alone.
He, Exalted is He, says when the Angels descended to reinforce the armies of the believers,
“Allah only did this for it to be good news for you and so that your hearts might be at rest by it; help comes from no one but Allah, the Almighty, the All-Wise” [Surah Al-Imran (3): 126]
“If Allah helps you, no one can vanquish you. If He forsakes you, who can help you after that? So let the believers put their trust in Allah” [Al-Imran (3): 160]
 Abu Dawud [#1518], ibn Majah [#3819] and Ahmad [#2234] on the authority of ibn 'Abbas.
The isnad is da’if as ruled by adh-Dhahabi [#7677], ibn Hibban as per al Iraqi, al-Mughni [#1027], al-Manawi, al-Qadir [#8508], and al-Albani, ad-Da’ifah [#705].
 al-Halimi al-Minhaj fi Shu’ab al-Iman, said, 'Hope takes on a number of forms: 1) hoping to attain what is desired 2) hoping to keep it after it has been attained 3) hoping to keep at bay all that is disliked and that it not occur 4) hoping to see the end of anything that is disliked that has already occurred. When the feeling of hope becomes deeply ingrained in a person, it leads to a state of submissiveness and humility in the same way that this state is achieved when fear takes firm root in the heart. This is because hope and fear go hand in hand, the one who is in a state of fear hopes for the opposite of what he fears - He supplicates to Allah and asks of Him; likewise the one in state of hope fears losing what he desires and hence takes refuge with Allah from this and asks of Him. Hence there is no one who is in a state of fear except that he too is in a state of hope and vice-versa.'
 At-Tirmidhi [#983], ibn Majah [#4261] and an-Nasai, Amal al-Yawm wal-Layla [#1062] on the authority of Anas.
Similar ahadith are recorded on the authority of 'Umar by al-Bayhaqi [#1003] and Sa’id bin al-Musayyab by at-Tabarani.
At-Tirmidhi said that it was gharib (and in one text hasan gharib), al-Mundhiri said it was hasan as per Tuhfatu-l-Ahwadhi [4/58] as did al-Albani, Sahih at-Tirmidhi [#785].
 Ibn al-Qayyim, while discussing the ahadith concerning taking medicine, says, 'These ahadith prove that causes and their effects exist and that to take to them does not negate tawakkul, just as it is not negated when someone takes food and drink to remove hunger and thirst. Indeed the reality of tawhid is not attained and completed except by taking to those means that Allah has appointed in order to attain their effects, to deny their existence is to impair ones tawakkul and to impute the order and wisdom of Allah with deficiency. To abandon these means is a deficiency that negates tawakkul whose reality is that the heart places its reliance upon Allah, Exalted is He, in attaining worldly and religious benefit and repressing worldly and religious harm. In order to complete this reliance one must take to the causes otherwise one is denying wisdom and the Legal Law, so the servant must not think that what is in reality deficiency is tawakkul and what is in reality tawakkul in deficiency.' - 'Abdur-Rahman Ali ash-Shaykh, Fath al-Majid [p. 60]
 For everything lawful that one may wish to acquire, Allah has appointed a means to attaining it as has preceded, for example marriage as a means to having children. If one marries and places his reliance upon marital relations and not upon the One who grants children, he has committed shirk; to deny that such means exist is to deny what is ingrained in our nature; and to deny that the act has any benefit at all is to accuse the Legal Law which has put the institution of marriage in place. The same applies to supplication, which is the reason why the author has brought up this principle.
 Bukhari [#32, 3360, 3428, 3429, 4629, 4776, 6918] and Muslim [#124]
 The author, Majmu’ Fatawa [10/185-187], says, 'Whoever depends upon an object of creation to help him, or provide for him, or guide him, his heart will submit to it and servitude will be engendered in it in proportion to the level of submission, This applies even if the person is a leader asking of his subjects who he controls, for the intelligent one looks to the realities not to what is superficially apparent. When a man's heart gives in to a woman, even if she be permissible for him, it becomes enslaved to her and whatever she commands, it will readily do, even though outwardly he is her master. The enslavement of the heart is more serious than the enslavement of the body and the servitude of the heart is greater than the servitude of the body... True freedom is the freedom of the heart and true servitude is the servitude of the heart just as true richness is the richness of the soul... when the heart tastes the relish of worshipping Allah, being sincere to Him, it will know that there is nothing sweeter or more delightful than this. Man will only leave one object of love for another if he finds that other more beloved to him or fears something distasteful happening. Therefore undesirable love can be removed by directing attention to desirable love or by fearing harm.'
Please write: COMMENT in this box to verify that you are human