Hi /u/cloakedbypeonies!
This is the core question of the field of [epistemology](https://en.wikipedia.org/wiki/Epistemology) which is a subsection of [philosophy of science](https://en.wikipedia.org/wiki/Philosophy_of_science).
Different schools of thought have given different answers to this question. The [Skeptics](https://en.wikipedia.org/wiki/Skepticism) radically doubted every empirical observation, the [British Empiricists](https://en.wikipedia.org/wiki/Empiricism#British_empiricism) countered with an empiricist positivsm while the [Critical Realists](https://en.wikipedia.org/wiki/Critical_realism_(philosophy_of_the_social_sciences)) reject positivism and focus on the understanding of causal mechanisms, to name a few influential schools of thought. .
Due to the immensity of this field, I would suggest reading into some of the articles linked above and formulating a more precise question if you are still wondering.
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