On more complex things, it's harder (and sometimes uncomputable) to come up with such precise probability estimates, but that doesn't change the principle. I believe with greater than 99% certainty that evolution happened. I believe with less certainty that Moore's law will continue for another two or three process nodes. I have very little belief that "psychics" can talk with the dead; equivalently, I have a very high degree of belief that they can not talk with the dead.
The degrees of belief we have about things should be revised upward or downward based on evidence, and should be based on the evidence we have available to us. Your belief that mars is real is supported by a lot of evidence, and therefore should have a high degree of confidence. But if I told you that there's a planet, unknown until now, called Uldune, and that this planet has space pirates using it as a supply base, then believing me with non-negligible certainty would be an act of blind faith. (Disbelieving me, with high certainty, would not be. My story about the planet Uldune contradicts a lot of evidence about the current state of the art in space travel, and the laws of physics, and so on.)