Sometimes one can get conditioned to conditions. On a recent trip to a familiar river (winter conditions), I was loaded for midge. Even rigged up at the truck. (Knew better). As soon as I hit the water, there were risers everywhere. Baetis not midges. Not the end of the world, because I had the right fly in my box.
I was conditioned to thinking "foot of snow on the bank, must be midges"
Two weeks previously it was only midges.