I decide the truth

This is something I wrestle with: if I decide what is the truth, how am I different than Donald Trump? There is science and history to use to make judgments, but science can progress and change based on new input. Just because history and experience inform high-ranking generals’ opinions and guidance, if you don’t try something new then how will you know if something new will work? Me deciding my thoughts and truth makes total sense, but when I see someone like this using a similar approach it trips me up. “I’m the decider” from George W. runs through my head ALL THE TIME.