There is a term of art that I either never learned or forgot, referring to an assumption in the context of estimating probabilities. I cannot find it in a quick search of Wiki on, for example, the Drake equation, which is the sort of speculative estimate I'm thinking of.
The term (if there is one) refers to the intuitively reasonable but unprovable assumption that an event which has occurred was more likely than not to do so, meaning, at a minimum, not highly unlikely. For example, if I assume that because earth has a good climate for supporting life, and since life arose on earth, then life is "quite likely" to arise given good conditions, does that general category of assumption have a name?