I have a very personal soft spot for hoarder!Haymitch. In the books, it's very clear his house is a biohazard. It feels so fitting. He's against self-improvement. He's against his own happiness. All he wants is to keep himself miserable as a punishment.
The moment Katniss and Peeta try to intervene and actually SUCCEED in helping him is so big. It's right before the third Quell. Right before everything changes. Right at the pinnacle moment where Haymitch becomes the driving force behind Katniss. It shows what's gonna happen before it does.
His house becomes livable again right before the arena. When he lets go of that need to be miserable, he instead focuses on Katniss and Peeta. Being there for them and trying to get them out. It just so happens that in the process he finds something else to live for.
The rebellion.
