The 25th Hour

Whenever something happens that disrupts the regular order or routine, it always comes along with a very intense existential questioning, sometimes working as a wake up call, reassuring or disproving previous values. When Monty is convicted, he triggers this questioning in all the people that are close to him, similar to the effect caused by the attack on the twin towers.
In the case of Monty, the most evident reaction is his wondering what could've been had he stopped drug dealing earlier, the life he could've had, all of this evidenced in his conversation with Frank at the club. Parallel to this illusion, there is a much more practical aspect to his personality and the need to have everything settled by the time he goes to jail. He gets Doyle a new home, settles (and ends) his business with the russian drug dealers, tries to convince Naturelle to live her life, basically, he puts an end to all the things belonging to his previous life in preparation for his time in jail. Monty's character shows an interesting dichotomy between dreaming for a life he can't have anymore and at the same time facing what needs to be done by separating himself from his feelings.
Meanwhile, Jacob, one of his best friends, seems to face important moral decisions regarding one of his students. He particularly questions what it is he stands for and the things he is willing to do, the bulk of moral questioning in the movie resides in this character. While at the club, he has trouble standing up to his student, which leads him to do things he normally wouldn't ever have done. Regardless, his moral crisis eventually leads him to reaffirm his values, staying true to what he portrays throughout the movie despite getting lost in the way.
Finally, there is Frank, who, compared to the other two, is the one who changed the most, or at least revealed the most about himself. He starts out as a cold character, someone who's full of himself and therefore doesn't really consider other people and their feelings, which can be seen especially when he goes out with Jacob. Although, as the movie goes on his outer shell begins to crumble beginning to show a much more fragile side to him, and also showing how much he cares about the people around him. The peak moment of this fragility is when Monty asks him to "make him ugly." At that point, all of the feelings that had previously been bottled up rush out, ending in frustrated tears and Monty getting beaten up. What's most important, though, is that Frank only starts beating Monty when he punches Jacob, which shows a significant change from the beginning, where Frank would bully and ridicule him in front of others, making it seem as if he didn't really care that much for Jacob.