I don’t know if this story is reliable, but it might be.
The Chazon Ish was told by Rabbi Wolf of a girl in his seminary who fell into a depression because of serious sins she committed before she came. The Chazon Ish commented this is what Chazal mean by “הרהורי עברה קשין מעברה”, Yoma 29b. The preoccupation with past sins can be more harmful to righteousness than the sins themselves!