The principle that certain things are they way they are because if they weren t that way, man would not be here to observe them. For instance, earth has.
The Anthropic Principle
How could the universe be so well balanced as to fall within such a very narrow band of laws that just happen to define the boundaries of human beings and their thought processes? It seems very unlikely. Therefore, Hoyle proposed that human beings originated and evolved within the universe because this is the kind of universe in which they could originate and evolve. It seems like circular reasoning, but it makes sense, in a philosophical kind of way. This kind of theorizing had a profound influence on Sir Hoyle. When he first began to think along these lines, he was an atheist, but he eventually came to believe that the guiding hand of God was behind the whole thing. To Hoyle, the statistical improbability of carbon-based life forms such as humans was too much to overcome. He could not imagine such an event without help from outside.