It is very important to keep in mind the experiences one learns a lesson from and holds up as an example; And the effects the important events one lives through create on his soul...

People come across certain incidents that very rarely happen in their lives. The profound effect of these incidents lasts for months or even years on that person.  The visions and voices about that incident never fade from their eyes and ears until the end of their lives. Such incidents like witnessing someone's death, sometimes an earthquake, a flood, a traffic accident, fire, sometimes a grave remorse, sometimes an event he feels very ashamed about, sometimes a very important and essential criticism he receives; may be among the incidents one can never forget until the end of his life.  

People generally grasp very essential truths while living through such incidents and take very important decisions. They find the conclusions they draw out of these incidents very important and contemplate "never to forget all these". They realize that the lessons they derive and the examples they hold up from these incidents are very precious experiences that will be beneficial for them until the end of their lives.

Along with such big incidents, sometimes some small and casual events might cause someone to take very important decisions. For instance when a person feels discomfort in his stomach after eating a hot or a spicy food, he would make a decision saying; "I will not forget this harm it caused me so that I would not eat something like that ever again." That is because he does not want to go through the same discomfort again.  However he might somehow forget this experience in no time at all. Or may be for someone, who failed his classes because of his laziness, becoming obliged to go to school one more year is in fact a very important experience for that person to draw a lesson from. May be he might think to himself at that time: "let me not forget the harms of being lazy" and contemplate not to make such a mistake ever again. Or a person who sees the destruction he caused on his relationship with a loved one, after a hurtful word he had uttered, would feel a great remorse. He will make a very sincere decision saying; "I will definitely think before I talk, I will never say the first thing that comes to my mind, ever again."  

There are some moments, like the ones in these examples, in a person's life which would make him grasp many points more deeply than ever. He makes decisions and says to himself "I will never do this again", "I will be very careful about this", "I will never use this word or this attitude ever again", "I will wipe this false point of view off my mind".  However the point here is that man is a very forgetful being. He forgets the little things in his daily life and the big incidents which take an important place in his life, along with the experiences he gained and the lessons he drew from those incidents and the decisions he had made, in no time. He might forget a point he had decided never to forget sometimes in a day or two, sometimes in an hour or two, and sometimes only in 5-10 minutes as soon as he gets distracted, until he makes the same mistake again.

Sometimes this repeats itself tens of times in one's life. An important incident or a mistake he made becomes an example for him to hold on and that person makes an essential decision about that point. But once he turns back to his normal daily life, he instantly forgets his decision.  In a short while he faces something similar. He says to himself; "I have faced a similar situation before and I have made a decision to behave without ever forgetting this experience I have gained from the things I lived through. But now I have made the same mistake because I have forgotten the decision I took. But this time I will never forget this decision." But he forgets nevertheless. And thus he gets himself in that position again.  He forgets it again. And again remembers the decision he had made before. And all these forgetting and experiencing similar things go on continuously.  

This situation would of course startle the person who experiences all these. He feels unable to understand why he cannot use his consciousness, his memory, his intelligence as he wanted to; and why he keeps making the same mistakes repeatedly about a point he knows very well and has made a resolution about.  

However, there is a very important prodigiousness that he should realize; "A person can instantly forget the things he experienced even on an essential matter that affected him deeply, unless he decides on it very sincerely and makes a very strong decision about it." What that person should do here is to search for the inadequacy in his intention.  

For instance if a man were to stand on an unprotected wooden ridge on the very brink of a big and deep pit of fire- with Allah's willing- his consciousness would be wide open. His forgetting that pit of fire would be out of question. The existence of the possibility of falling down from the wooden ridge he stands on in any minute, would cause this person to reach the highest level of vigilance.  There would be no need for anyone to remind him the position he is in, or for him experiencing the same thing all over again.  He would have the necessary mental capacity to be able to think about and do everything that would protect him from danger and from falling into that fire.  

If a person fails to act according to a decision he had sincerely taken at that moment even though he had previously lived through an experience which affected him deeply; the problem there is, that he finds other matters more important than this subject. The reason why his attention gets distracted in other matters is because he takes a greater interest in those matters.  

Consequently if a person continuously repeats a mistake he made and does not get adequately affected from the spiritual and material damage and destruction that mistake causes on him; or if he fails to draw the necessary lesson from the exemplary incident he experiences and gets himself into the same situation over and over again; he should consider the fact that there might be a sickness in his conscience and try to reinforce his conscience.  

However, of course, forgetfulness is a very important weakness of man. A person- unless Allah wills so - cannot prevent himself forgetting something. But he can strive with all his might not to forget. He can take every material and spiritual precaution one might think of.  He should not say "I am a weak human being, I would definitely forget even if I take all the precautions", and be aware of the fact that it is Allah Who will create the result he hopes for, if he strives for it.  He should strive, with all his might, not to forget the effect of such experiences and the importance of the decisions he had taken.  He should concentrate all his attention in attaining the moral perfection for the approval of Allah.  

Despite of all this effort he showed, if he forgets nevertheless, it could be that Allah would not deem him responsible for forgetting.  And Allah might pave the way for that person nevertheless.  

It has been revealed in the Qur'an that Muslims making a sincere effort like this beseech Our Lord for not 'taking them to task for what they forget and for their mistakes' as follows:
 

Allah does not impose on any self any more than it can stand. For it is what it has earned; against it, what it has merited. Our Lord, do not take us to task if we forget or make a mistake! Our Lord, do not place on us a load like the one You placed on those before us! Our Lord, do not place on us a load we have not the strength to bear! And pardon us; and forgive us; and have mercy on us. You are our Master , so help us against those who stand against faith" (Surat al-Baqara: 286)