I keep a graveyard file of dead ideas and it's my most useful document

Every idea I've tested and abandoned gets three lines: what it was, what I expected, what actually happened. It's stopped me re-testing the same thing four times, which I definitely used to do. It's also shown me a pattern I'd never have noticed otherwise — almost everything I abandon dies for the same two reasons, which tells me something about the kind of idea I'm drawn to. Takes two minutes per dead idea. I have about ninety of them now. It's the only research document I actually reread.