If we are to study , why human are able to think independently , we go to the brain.Now, when you study the brain and view it from a philosophy spectrum, you will see that the brain is simply a bunch of chemicals ( in fact, everything is chemicals ) that collaborates together and form a very sophisticated and complicated active mechanism of maneuvering and solving variables of countless many ( think of it like this , you mix in a mixture of chemicals ( such as H(2)O,CO(2) and all kinds of other chemical component of the brain) , and find that the mixed chemicals are capable of thinking!).As quoted from Oliver Sachs from the TED Talk ( forgive me if I'm mistaken),"Information in the form of energy , streams in simultaneously through all of our sensory systems , and then it explodes into this collaborative collage ( the collage here are used to signified the greatness of our brain , being each of the brain cell ability to think )".
Now , our brain has two very opposing parts , the passive and the active group.This two groups are very different in a manner such that it can even contradicts itself , although it being in a single organ in our body which is weird.That is the power of decision.
We make decision in our daily life and in fact , every things make decision , even in the atomic level ( the attracting and discharge of electron itself by atoms is decision).But what makes us different from other things are that we are able to make decision even beyond the passive limitation ).For example , when you are running you will eventually gets tired.When you are tired , your passive group of brain make decisions to increase heartbeat and increase breathing process rate , and provide your active group of brain