In order to be able to identify the causes of being afflicted with sins and committing them, we should pay attention to the causes of these sins, noting that there are many causes and factors. We will only mention here two main ones:
1- Weakness of Self-belief:
The most important reason for committing sins is the weakness of the religious deterrent in man, or what is called “weakness of faith”. Faith is a matter that accepts increase and decrease, strength and weakness.
We see in our society many people who complain about the hardness of their hearts, and their lack of reverence in their prayers. We also see them behaving with eagerness for the world, and with despair and sadness in harsh circumstances and calamities. This is added to selfishness, vanity and fanaticism and many other diseases which are all related to one cause, which is the weakness of faith. This cause increases and intensifies through acts of obedience and decreases and is weakened by disobedience. “Whenever a Surah is revealed, some of them ask ?mockingly?, “Which of you has this increased in faith?” As for the believers, it has increased them in faith and they rejoice, But as for those with sickness in their hearts,1 it has increased them only in wickedness upon their wickedness, and they die as disbelievers” 
There is no doubt that this weakness or strength of faith is not born with a person, and no one is forced to be so since this contradicts the principle of choice and the doctrine of “choosing a matter between two” which means denying compulsion and delegation to people, and affirming the optional assignment that the School of Ahl Al Bayt (pbuh) believes in. Through this statement, we understand that there are reasons that lead to the weakness of faith, or even lead to its fading out in some cases, as if it does not exist.
What are those reasons that may lead to the erosion of faith and that lead a person to commit sins and disobey God?
Among the main reasons for the weakness of faith:
- Ignorance and lack of knowledge is one of the greatest causes of weak faith.
- The predominance of passion and prolonged hope, for the predominance of passion makes a person inclined to desires, and prolonged hope makes him forget the Hereafter and attract him to this world.
- Accompanying fools and immoral people.
- Going to places of sin.
- Leaving the Quran, and not going to mosques and holy places.
- Not sitting with scholars and people of worship.
2- The control of desires and instincts over a person:
It means a set of instincts and forces that exist within the human being. If he does not know them and does not seek to modify them, it will lead him to inevitable doom and falling into sins. He must first know them and strive to modify them, which means to get it beyond the limit of excess and negligence because failure to do so will lead to its tyranny and instability. This is what will push a person to commit sins.
These inner powers deposited in a person may affect his behavior and his relation with God almighty, negatively or positively. God Almighty created in man “the power of reason” and provided soldiers for this power. On the other hand, He created in him the “power of ignorance” as well and accompanied it with soldiers.
A man in his ascending mental movement may reach a level higher than that of the angels if he abstains from commiting sins by his own free will, choice, judgment of his mind and control over his instincts, as God almighty says in His holy book:” They are only like cattle—no, more than that, they are astray from the ?Right? Way”. This is because a man lets his desires control his mind and follows his instincts and psychological desires.
Guidance and Good Tidings, Al Maaref Islamic and Cultural Institution
 Surah Al Tawbah, verses 124-125
 Surah Al Furqan verse 44