Working on really unclear code, like bad style, architecture, encapsulation...
Having to consistently write such code due to time constraints is even worse.
I don't mean the occasional pressing deadline or small mistakes, but code that is almost impossible to read and any change will have unpredictable side effects all across the system.
You know it's just going to be less maintainable every month and will eventually be 90% bugfixing with few new features. Not really motivating to contribute to such shortsightedness.