Answer: Nothing is erased or lost. A person doesn’t remember his previous lives because he has never left his body, which means that he has not yet reached any spiritual attainments and therefore doesn’t feel anything beyond his body.
But nonetheless, all of a person’s lives will return to him in any case. It doesn’t mean that he will reveal them, but all the past experiences will be revealed and cleared up to him, and by that a person will be able to reach the upper world.
From the Kabbalah Lesson in Russian 12/20/15