Say you have just realized something that seems, in hindsight, pretty obvious - but that you were totally unaware of before now. You scratch your head, update your model of the world, and move on.
Hold on. Update your model of your model. Why were you not aware of it before? If this insight, in retrospect, seems so basic, then why did you not realize it earlier? And how many other people do you think missed it as well?
There is a common situation in user interface development, where you've written a marvellous, clear, easy to use piece of software - after all, you have no problems with it at all! You've stuck to the practice of dogfooding ("eat your own dog food" - use your own tool in day to day life) like a good developer should and are now quite faster in it than in whatever you were using before. So find a random coworker who has never touched your software before and may only be passingly familiar with the subject matter. Put him in front of your shiny user interface and watch him waddle around, dumbstruck and befuddled, as he misses all the obvious interface elements and tries nonworking things you'd never attempted in a hundred years. Resist your urge to correct him - pay attention to what he tries.
You cannot judge the obviousness of an idea from the inside - you have to find somebody without prior exposure and observe them attempt to come to terms with it, to understand. And it only works once - after he's become familiar with your idioms, he'll never be able to show this bright-eyed naiveté again.
If you're trying to write a FAQ for life, it'd be very much helpful to have such a coworker go over your life, re-learn all your lessons, all the insights you now consider obvious, and highlight them so you could add them to the help file. But of course, we cannot relive a life. We can only live it once.
So the obvious thing to do is when you realize that you've just had a novel realization - no matter how apparently trivial - is write it down. The brain is really good at caching - realizations become thought habits frighteningly fast. So write it down, so you don't forget that you once had no idea. And after you've written it down (probably on a file on your PC), why not share this file with the world? Might as well let others profit from your insights.
I think it would be useful to spread this habit. Imagine: somebody just did something really clever that raised your estimate of their competence, and oh hey, his user page has a link to a list of insights, maybe I can skip having to manually learn some of those myself? And look, the first piece of advice - "write down your insights", that sounds like a good idea!
It's not proven that this would be useful. But it costs little to start.