The, "Oh gawd, what have I done?" feeling that kicks in within the last 5 seconds.. (Thinks - what does everyone else know but not me?)
I know that one well.
About 15 years ago I chucked a random £100 bid in for an Electrocoin Spectrum arcade cab with Carrier Airwing. Forgot I bid on it and ended up winning! The seller even chucked in delivery for free as he was delivering some pool tables in the North East!
My parents were gracious enough to let me put it in the dining room. That would be worth about £7-800 these days, with delivery on top! Didn't know the first thing about how arcade cabs worked