1) The amount of evidence for a claim. 2) The grandiosity of the claim.
If you tell me you have a pet dog named "Spike" I probably would be willing to accept that with as little evidence as a picture of you holding a dog, found in your wallet [i might even take your word for it, if i knew you to be an otherwise mostly honest person]. Because, dogs exist and are plentiful, billions of people own dogs, and "Spike" is a common name. you may be fooling me (it may be the neighbors dog) but i'm still justified in the believe because the evidence rises to the claim.
If on the other hand you claim that you have a pink polka dotted flying dragon as as a pet named "Chester". I would be a fool to believe you. I have no evidence such a thing exists, or that people have them as pets. I would have to see it in person, and even then, i would need to get a report from teams of biologists/zoologists to be willing to accept the claim. It would require tons more evidence.
And yet, the claim STILL isn't _that_ preposterous. The dragon would be an animal, and i know animals exist. I know there are animals with scales, i know some animals fly. I even now there are some with wild coat patterns.
Now if you tell me you believe in an all powerful all knowing god who is responsible for why there is life? I have zero evidence, i have no experience like what you are describing. I've never been given evidence of a being outside of time and space. I don't know that that is even a thing. I don't know what all powerful is, or if that could exist? or all knowing? is that possible? I have no correlary to compare to. It's not like we know King Neptune exists, and while not infinitely powerful, is still pretty boss. Why would i believe that was the explanation for why there are creatures on this planet?
Evolution, on the other hand, has mounds of evidence. We have a powerful fossil record, We went thru a pandemic that shows the power of mutation. Even our own ability to drink milk. And yet even evolution isn't making all that fanciful of predictions. It doesn't claim to know your thoughts, or how you will die. So the evidence rises to claim. Do we know everything there is to know about evolution? Could we be wrong in some areas? Sure. But we are justified in accepting it.