[Dr_Acula]

The whole thing is potential. Suppose you have two possibilities, so they both have potential. But what is potential? Ignorance. It refers to what you don't know, and therefore you are uncertain which decision will prevail. But then the decision is made and only one possibility prooved to be really possible, and the other one was never really possible. You just didn't know, you didn't have enough knowledge, so you were forced to say that both had potential. If you knew all the facts, then you would see that only one option will happen.

Some said that free will is having potential in various decisions. But potential is nothing by itself, it's just a way of representing ignorance. In this sense, it could be said that the strict definition of free will you gave is indeed an illusion.
Yet still, lets not forget that the decision made was the one that prevailed after the individual assesed the situation and choose the course of action that HE decided was most suitable, so in that sense, it was still the will of the individual, free or not.