Don't be afraid sometimes to write something easy, for practice, for relaxation, for a break, or just to see how well your writing skills are holding together. Conversely, sometimes you have to tackle what you're afraid to write or what you think you're not good enough to write. That's how you grow as a writer. At times like that, maybe you're better off just running with it and damn the consequences. I plan all other activities for the late afternoon and evening.
Expectations are important.
Make expectations realistic. Expecting you'll get to write in a situation where you probably won't will make you crazy. It is a basic truth that the person who quits climbing won't get to the top of the mountain. If you want to get to the top of the mountain, whatever that may be, keep putting one foot after the next. It's the only way.