Unfortunately, people have gone through all kinds of negative experiences. How can we truly forget about all that we have gone through in life?
It is not possible to forget completely. What is possible, however, is that a person can sit with himself in a calm silence, and allow his thoughts to roam. (The thoughts should be allowed to blow around freely as if they are floating above the surface of the water.) For every thought that comes to you, allow the thought to continue. Become aware of it, and allow it to continue further. Let it roam, and slowly, slowly, a person will then feel that his mind has been quieted and emptied. [So] you should let the thoughts roam freely during a time of quiet, without disturbances.
This is not a way of totally forgetting [about the bothersome thoughts], but it is a way for a person to return to a calm place in the soul. When you then enter the quiet place in the soul, [you will discover that] this inner place in the soul has never experienced the bothersome thoughts. It has remained clean [pure and undisturbed] all along. But in order to reach it, one needs to quiet all of his surroundings, and then he can reach this [inner] place [in his soul] which is clean [pure and undisturbed], quiet, and relaxed.