Apparently the point is missing you. It is trivial to prove that it COULD have happened, regardless of whether it DID happen. By establishing a non-null prior, it becomes rational to believe your assertion that you fell down the steps as a child taken by itself.
And as is in rampant evidence, people make up bullshit stories about things all the time, either through stupidity, malice, or simple ignorance. In the absence of a non-null prior, we have NO reason to believe a word of it.
Yes but his point is this "If something happened but you can't prove it to someone else, it really didn't happen". And that is Reason???