This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Looking for Group
Page 355, where we learn that not only was Cale's wife forced to drive him away, but she was killed to make sure it stayed that way.
Pretty much any character reaction to Krunch's death counts, but the final twist of the knife has to beBenny trying desperately to resurrect him, putting more power into the spell than anything we've seen from her before that point, and the resulting breakdown when she realizes that no matter how hard she tries, she cannot bring her father back.
Page 589. What starts as Richard being, well... Richard, becomes sad and incredibly disturbing by what he's implying. He doesn't want to kill innocent people anymore, and seems to believe that, by killing the Book of the Innocent, he won't have to. A very unsettling Out-of-Character Moment for the homicidal warlock.
Page 613 seems to confirm it. Richard is desperate to break the curse, having to frequently remind himself of what he was like before.
Page 782 implies that the Archmage destroyed Richard's life much as he is attempting to do with Cale.
Tim NPC's story, in the first part he lost his adoptive parents while Styx vow to protect his mentally challenged big brother from harm. In the second it is implied that Tim had regular intelligence until he got hit too much with maces and Styx wonders if he even remember the old days.