One way to deal with it is to understand why the mess in the first place. You may find reasons to forgive the mess. If you're looking at a startup that had to try a lot of things perhaps (and when the team was junior) hitting on the workable idea later, maybe they just did what they had to do. The forgivance may also give you the incentive to improve it. A good measure is whether the shitty code does something worthwhile and interesting. Might get you to a point of empathy.

Edit: "you" = OP