Because there is no evidence in any of the complexity in the universe, that it comes from something less complex, we know that complexity must come from something at least as complex.

Since there is no complexity in the universe that we see coming from something equally complex, what is left?

Since we know that there is no real random because everything comes about by cause and effect, what is left?

The only thing that is left is that complexity comes from something more complex.

Science bears this out. Two people of opposite sex are more complex than one person. Why? The one person has only one sex. Even if the person is Bi, the two are still more complex than the one. Only less complexity comes from greater complexity.

Or take a car for example. The car is complex. But the people who made it are way more complex.

There are so extremely many of examples of less complexity coming from greater complexity, and no examples of greater complexity coming from lesser complexity, that this is a law of the universe... at least until someone proves it wrong. They need to start by finding even one example.

The complexity of the universe, and of the brain and mind of man, was made by greater complexity. And since man, complex as he is, barely knows how to extend life a little, the complexity that made life must be way beyond the complexity of man and the universe.