What I don't understand is how they can be so picky with flies, and then take a spinner which doesn't look like anything in the water.

edit..Spinner being the lure type. Not the fly.
What's worse is watching a fish repeatedly take a certain type of bug, matching that bug perfectly, having the fish refuse your bug. Giving up and tying something on that doesn't hatch for 4 weeks and having the fish take on the first drift

I think they've got a descent short term memory, but I doubt they have much of a long term memory