- When faced with a problem you don’t understand, do any part of it you do understand, then look at it again.
Heinlein, of course: The Moon is a Harsh Mistress
Yes, this algorithm can stall you at a local maximum, but that’s better than remaining stuck in the starting gate while you’re thinking too much.
In less high-falutin’ terms: Don’t just sit there, do something!
The Smell of Molten Projects in the Morning 
People keep on quoting this over and over again. It’s a good one, of course, but it almost seems like it’s becoming one of those annoying Internet memes. Or perhaps it’s just the parts of the Internet where I hang out. ;)
In my defense, I’ve known that one since shortly after that book came out in the mid 60s, long before there was even the possibility of an Internet meme. So I’d say everybody else is just getting around to noticing a good thing. [grin]
Turns out our copy of TMIAHM was signed by Heinlein; we got it as part of a fundraising thing for the L5 Society, back when they weren’t the NSS… and when we shrank the library a while ago, we unloaded the much older copy I’d had since forever.