“Multiplication.” That is, the notion that you actually can compute expected value of real-world choices. Most blandly, I won an iPod in a raffle after a very rough computation that buying tickets was actually worthwhile compared to buying the item at retail, whereas I had previously been ‘irrationally’ opposed to anything resembling ‘gambling’.

This. One time my grad school department wanted to have the most donations to charity through the university's program, and so they arranged that a donation of any size (even $1) would constitute an entry into a department-organized raffle-y thing. I don't know where the prizes came from, but instead of dismissing the prospect out of hand I did a little arithmetic, got an estimate of how many people were entering from the school secretary, and determined that the cash prizes alone (let alone the gift basket and whatnot) constituted positive expected value. So I gave Planned Parenthood a dollar. (I lost, though.)