I don't think that even a person who tries can 'know' any more than 'God exists'. Anyone who would claim even that much knowledge (as I do) must accept that its validity is limited to oneself.

That applies, for that matter, to all beliefs (assertions of knowing that are not amenable to validation within material existence): every belief of every person is absolutely valid for that person, but of no consequence whatsoever for anyone else. If everyone would accept that simple truth, this world would immediately become a more pleasant place.