When we are talking ranges your not going to make a bang on decision on what marble he has on the first try. But if you pull a marble out of the bag 1000 times you will know what he has in his hand. Think of it this way, if he pulls a red marble out of the bag, and you pull a marble 1000 times you are going to pull more blue marbles than red, about 2:1. Basing this on information provided, you know that there are only three marbles in the bag, and he has one in his hand. If you were to bet that you could guess his marble, you will be right two out of every three times, which in turn is an EV call for you. Same with cards, if you figure someone to have either AA or AK or even KK, what is on the board and what is in your hand will allow you to base this information as MORE CORRECT over the long term.