Rationalism fails because human behaviour is irrational and most things now involve human behaviour as at least a part. There may well be reasons we do things or are part of things but rationalism cannot explain them. However, that is not to say that religion any better describes what we do or why things happen. Irrationality is just a part of the natural make up of people. Religion tries to appeal to it while rationality tries to explain it away or demean it. However, what is natural cannot just be disappeared in this way and any attempt to appeal to it is just an attempt to use a natural condition for ulterior reasons. Irrationality is just part of the human condition and should be accepted as such.