When you get into the mindset of "I'm going to write some poetry tonight," you start thinking in lines, and, if you're corny like me, you end them all in rhymes.
But then, while you're doing some innocuous thing, like peeing, you find yourself thinking of something that you think might sound pretty great.
Then you sit down to type it out, but they've all gone away.
Like a flock of birds, as soon as you sprint to catch one, they all dissipate.
You're left there empty-handed, wondering how you're no longer comprehending some amazing string of thoughts that had flown through your head just moments ago, now so far beyond your understanding.
I thought of a good one earlier about the difference between appealing to the masses from appealing to a more eclectic audience, but then when I tried to think of it a second time, it completely eluded me. I'd even gotten as far as thinking of a name for it (which always comes last.) I was going to title it "Niche"