I don’t believe in optimism. I believe in optimal behavior. That’s a different thing … Action is hope. At the end of each day, when you’ve done your work, you lie there and think, Well, I’ll be damned, I did this today. It doesn’t matter how good it is, or how bad – you did it. At the end of the week you’ll have a certain amount of accumulation. At the end of a year, you look back and say, I’ll be damned, it’s been a good year.
What Bradbury is talking about here is building good daily habits and letting the numbers game take it from there.
If you start every day with a writing session, and if by some miracle you can figure out how to lose your attachment to the quality of your work each day, you will write some truly good stuff. It's inevitable--a mere matter of time. Be patient and stick with it.