The Kelly Criterion is when you're betting with something that you value logarithmically. That is, doubling it gives you a constant utility. As such, it's not an even bet. For example, if you have $1500, and you've already bet $500 and you're considering betting another $1, you're comparing gaining $1 when you have $2000 with losing $1 when you have $1000. Since the dollar is twice as valuable in the second case, you're actually betting at 1:2 odds.

Also, the Kelly Criterion limits the amount you're betting based on your certainty. You still bet something.