the instacall

One thing I have to start eliminating is the instacall without the nuts. On this hand, I nearly instacalled the river bet. On the flop, I put him on an overpair, like 88 or something like that. But would 88 really shove on me on the river? You'd have to be a real donkey to do that. But here we are - an instacall with the worst hand. Why can't I think these things through?

http://www.pokerhand.org/?2800329