I agree completely with firebones. Getting a pocket-sized Moleskine notebook last year and jotting down observations that arise when I interact with the world has been most helpful. One surprising point is that looking back on my notebook, many ideas I would've forgotten about completely if they hadn't been written down. I'm not saying these are $1M ideas, but it's nice to have a record of what you were thinking 6 months ago.

To borrow pg's analogy that we are the executable whose source code we've lost, by writing down our thoughts (even in point-form) we may at least hope to generate output logs of versions of ourselves compiled at different times.