Being certain of something or asserting it as fact is not the same as saying every possible explanation no matter how unlikely is considered. I mean I also cant prove we arent sitting int he matrix and Biden isnt some sort of computer program.
When we assert certainty, even a doctor, we do so "beyond a reasonable doubt". I am certain "beyond a reasonable doubt" he had dementia, and I turned out to be correct. Does that mean there isnt a 0.000001% chance it is something else... sure, but no one talks like that. Nothing in life is ever certain without any possibility of doubt of any kind. But once it is past a certain threshold we talk and interact as if it is an absolute fact, as well we should.
Whats more important to me is my track record.. When i have high confidence does the percentage of times i turn out to be right match my confidence. If so, it is well founded.