This unidentifiable and yet sufficient cause that Ree attributes all actions to is no more evident than the argument or proof for God.  Because if we accept causality as a universal law, it does beg the question as to what then is the first cause of all these other invisible and complex causes. Ree provides us with no answer here. However, Sartre answers this question and accounts for it in his argument by noting that we are our own first cause, that we define our existence and therefore have freewill.