See footnote 2.

My favorite story along these lines (that I bought for $20):

I'm walking through Atlanta when I'm stopped by a man who seems likely to be homeless. He compliments my shoes, and tells me that, even beyond that, he recognizes the kind of shoe. He bets me $10 that he can tell me the city and state where I got those shoes.

I stop and think for a moment. $10 is small enough, and I'm curious to see what the trick is, so I agree, but ask for a few seconds to remember where I got the shoes. He nods and patiently waits, then I tell him to go ahead. He launches into a clearly prepared speech, which ends with "Never play a man at his own game. I didn't say I'd tell you where you bought, purchased, or acquired those shoes- I told you I'd tell you where you got them. And you got them on your feet in Atlanta, Georgia."

I smiled, pulled out my wallet, and didn't have a $10 bill, so I gave him a $20.

(The gum example is a great way to trick your friends, incidentally- most people's intuitions are wrong about which side is more likely.)

This is discussed in footnote 2. (And focusing on this problem isn't in the spirit of LCPW.)