Hidden vs open strength is part of the story here.
Running bad is the other part. I recently had a run like this.

Set of 2s on a AT2 board, turn T, river T. I fold to a $30 all-in bet into a $150 pot.

Guy raises 3x UTG after just losing a big pot, I call with AJs, medicore player over-calls. Flop is AJT. Titly checks, I pot it, medicore min-raises, I put in half his $60ish stack. Turn is a K and I can't see not putting the rest in with a card to come. Medicore has AK.

...and so on. IT happens.