Indeed there's bad days, and as you correctly said; The good days wouldn't be appreciated as much without them. It's where you get the perspective. So... should you 'cure' yourself from bad days? No, they're there for a reason, too. But that doesn't mean you can try to make the best of a lousy day as well.

Keep smiling... but don't be afraid to cry from time to time as well. It's just as important to sometimes... just let it all out!