The sentence "Your choices are half chance" means that the decisions you make are based on luck or randomness, and there is only a 50% probability of success or the desired outcome. Here's a rephrased version: "Your decisions rely on a toss of the coin."

It's not a very natural phrase. 'Chance' normally means that it's random, left up to probability, or guessing. So if your choices were 'half chance,' that would mean the person is basically guessing, making uninformed, random, or poorly thought out decisions half of the time. It depends on what the context of this statement was. To some degree, it's true, as we don't ever have complete and accurate information, we operate on biases, and perhaps the choices we make are as good as guessing. Or, if it was said with a negative intention, it could just mean the person makes poorly considered decisions and leaves things up to 'chance.'