Those great ideas that come while you’re jogging? Write ‘em down or you’ll lose them — and worse, you may dry up the well of ideas. If your brain notices you’re not paying attention to the good ideas it generates, it may decide to stop bothering. And then you’re screwed.
So always carry a pen. Pick up a piece of paper trash. Write on your hand if you have to. It’s often just one or two words which will let you remember what the idea was.