You can’t know anything (not with any absolute certainty) unless you know everything that there is to know because there could be something that you don’t know that could refute what you think that you do know. So unless you know absolutely everything there is to know then you really can’t know anything. Unless of course you know the one who knows everything, i.e. the God of the Bible (the one true and living God).
“The fear of the LORD is the beginning of knowledge: but fools despise wisdom and instruction.” - Proverbs 1:7