I assumed you'd already factored in those other choices and still weren't leaning more for or against it relative to all the other possibilities combined. By "leaning one way or another", I meant along a hypothetical axis of "strongly believe" or "strongly disbelieve" for the given proposition. You have a good point about availability bias though. You can self-correct for that to some extent by decreasing your assigned probabilities, and we'd have to take availability bias into account while interpreting the probabilities given by other people.