The key element of pot odds is how they compare to drawing odds. Say you have 4 to a flush after the turn. Your chances of hitting that draw are 1 in 5. If there's 100 in the pot, and somebody bets 50, you need to pay 50 to win 150, 3 to win. So that's a bad call, taking a 1-5 chance to win 3-1. On the other hand, if the bet is 10, then you are calling 10 to make 110, 11 to 1. So that's a good call, taking a 1-5 chance to win 11-1.
Think of it in terms of betting on a coin-flip. A coin flip is a 50/50 proposition. If somebody offers to bet their quarter against your dollar, you are giving 4-1 odds on a 1-1 proposition, a bad bet. If somebody offers to bet their quarter against your dollar, you are getting 4-1 odds on a 1-1 proposition, a good bet.