Free will is not tangible. When one says that they will choose A to happen over B, and A does happen, A is the only possible occurence, since only that happens, and B does not. To say that B could have happened is to say that you could have not read this debate, but obviously you could not physically resist the impulse to do it. You cannot un read it.
The pre-detemination concept is interesting. The same concept can be found in a kindergarden class, but not as a childish scenario. For example, Billy says he can do magic so Joey is interested to test the authenticity of this claim. Billy says pick a card. Joey takes a card. and puts it in his pocket. Joey says, "if you really can do magic, then you know what the card is in my pocket. So what is the card?" Knowing tat magic does not actually exist, but is an illusion, Billy states, " You have to give the card back so i can finish my trick." Joey says to Billy, " No." and rips the card to pieces and throws it away. Now Billy states, "i knew you were going to do that so i didn't actually know how to do the trick, i just wanted to see if you would believe me." Saying an action or effect of a cause was pre-determined would not only disprove the reason for life but show the very denial for the human's instinct to explore and expand. This is so humans can determine their own future and fate.