What allows for probabilities to be calculated at all?
What is being tested? What is being measured?
Putting numbers to something is not difficult. With the right mindset, anything can have a number tag and be compared in some linear fashion, so the mathematics of “likelihood” is nothing special, although given the fascination with “game-of-chance” from which probability arises and never left (the Fates) one might think it underlies the Universe itself.
But does it?
What’s being measured? Is it likelihood?
I don’t think it is.
What’s being measured is entirely human and in the realm of rhetoric, akin to court proceedings.
Probability is a measure of convinceability. Can I convince another human?
So, this notion of “what is reasonable?” is not an axiomic function, no more than an engineering rule of thumb or “a stitch in time saves nine” are universal truths.