Why do we do the things we do?

At first glance this may seem a rather odd question. Surely there must be a reason for every action? If so we could then narrow it down to "well it seemed best at the time". What if it wasn't best? What if our reasoning is flawed? In such a case one would lurch from one circumstance to another never achieving what one hoped for, in fact life would be a constant struggle, (does this sound familiar?). I will put forward an argument that in fact there is only one reason why we do anything and because that reason is wrong the action is wrong and the result not what we hoped for.