The greatest difficulty the modern ba'al teshuvah is likely to face arises when he tries to ignore his past altogether.
Doing so can have some apparent benefits, but also carries with it the dangers of self-satisfaction, smugness, and impatience with the difficulties of others.
One becomes callous and insensitive, losing sight of the fact that people differ and that those who are different are not necessarily worse.
It is only by remembering one's own past, by seeing the past as an integral part of one's life, that one can make the proper assessments.
Though the ba'al teshuvah may now find himself in a "different world," he must remember that he was not always there and that he is still responsible for what came before.
–Rabbi Adin Steinsaltz
From "Teshuvah in the Modern World" from Teshuvah: A Guide for the Newly Observant Jew by Rabbi Adin Steinsaltz