Imagine a town. Maybe an early New England village.
There is a dominant belief in this town that one must attend church every Sunday if they want to live a prosperous life.
Because the belief is pervasive, those who want to be prosperous attend in high numbers. Those who don't care about being prosperous attend less. Since those who care more about prosperity choose church more than those who care less, if you were to look at data on the prosperity level of the townspeople, you'd find that those who attended church were more prosperous than those who didn't on average.
This would provide further fuel to the idea that prosperity requires church. It would be considered a must, not even worth questioning. Even skeptics would say things like, "It's not the only or main cause of prosperity, but you'd better attend just to be safe and decrease the odds that you don't succeed."