Actually, it's NOT true that you should always exchange the envelope
after you open it. You should do it or not depending on the amount of
money in the envelope. (But for which amount of money I should
exchange, and for which amount I shouldn't? This is where the ***
comes from) However, once you average over all possible amounts of
money, the final answer for whether to exchange or not before you open
the envelope is always "don't care".