how much should you believe something? after all evidence

Instead of having a binary approach : how much extend you believe?

Untitled

https://www.youtube.com/watch?v=HZGCoVF3YvM

https://www.youtube.com/watch?v=R13BD8qKeTg

Your degree of belief in a hypothesis should be determined by how likely the hypothesis is beforehand, before you even look at the evidence. If the hypothesis is true, what are the odds that you would see the evidence that you are seeing, scaled by how common is that evidence across the board whether the hypothesis is true or false?