If all the things that people prayed for happened...

Even if all the things that people prayed for happened - which they do not - this would not prove what Christians mean by the efficacy of prayer. For prayer is request. The essence of request, as distinct from compulsion, is that it may or may not be granted. And if an infinitely wise Being listens to the requests of finite and foolish creatures, of course He will sometimes grant and sometimes refuse them. Invariable "success" in prayer would not prove the Christian doctrine at all. It would prove something more like magic - a power in certain human beings to control, or compel, the course of nature.

C. S. Lewis (1898-1963), The Efficacy of Prayer