Fine Tuning Principle: Devastating Disproof and Scientific Refutation of Atheism.

[Angrboda]

I doubt that anyone can guarantee we're in charge of the other 5, either.  If 5% is the optimistic scenario......

Agree. 
In making a decision today one is totally constrained by the neurological electrical patterns already established in the brain. 
One can decide (perhaps using a "rarely used" pattern) to change a behavior pattern and work on that. That is a possibility ... seems to me.

Free will is a strange belief. People intuitively believe that they act upon the facts and already existing mental content. So where would freedom come in?