In other words, assumptions and preconceived notions about what being a writer is all about are the things that kill productivity and sometimes even stall a career. Trust me. I know these things from the inside out.
In her Write Better Faster productivity class -- which I cannot recommend enough; it is literally life-changing -- Becca Syme encourages writers to always "question the premise" (QTP). To put a few of those aforementioned seven-deadlies through the QTP wringer:
1. I should write every day, at least 500 words.
2. I could finish a book. Real fast, even, and it would be a bestseller. Anybody could.
3. A good book can't have prologue or flashbacks or a dream sequence or a scene where the character looks into a mirror or a scene where the fantasy hero wanders off to gather herbs or ... etc.
or, perhaps worse
I can't write as well as [some other person]. I can't get an agent. I can't write in the genre I want to because it's not selling. I should put my first manuscript into a drawer, even if I think it's pretty good because the first manuscript is always crap.
and worst of all
All the others lead to that last one, and it's a doozy. Just remember that all these premises are lies, and lies kill [productivity].