It's like the who stole the cookie from the cookie jar.

Say, person A actually took the last cookie. Person B goes to take one but finds there is none. The only suspects must be person A and person C (let's say, person B was out all day).

Because person C adamantly insists they did not take it, and knows in themselves there was no posibility they took it, person B believes person A -must- have taken it.

Sure, C is telling the truth, but how DOES person B know this? Surely that would depend entirely on how much trust they have in this person, how well they know them, etc.

Yes this has happened to me. Yes I am person A.