How it feels depends on the situation. If the piece of data is something I should know that is critical for doing something, I'll kick myself, smite my brow, and say "D'oh!". If it's something I always meant to find out about, and whoever asks me knows about it, it's a good opportunity to sit back and be enlightened. Let them shine. Then cross-reference it. For esoteric musings that no one handy knows about, there are reference materials of all flavours.
I just keep chanting to myself "It's okay not to know everything as long as you know where to look it up." That way I only have to know a lot of things off the top of my head to retain my self-respect.
Not Knowing or Having Forgotten
I just keep chanting to myself "It's okay not to know everything as long as you know where to look it up." That way I only have to know a lot of things off the top of my head to retain my self-respect.