The field known as Epistemology. Central issues include: whether we can make a meaningful distinction between knowledge and opinion; whether there is such a thing as certain knowledge; whether knowledge is relative to the knower.
Exploring what it is for a claim to be justified (and thus becomes knowledge); does all justification stem from experience, or does the power of the mind – reason – play a role? Could there be a justification through reason alone that does not require a reference to experience (the case of mathematics)?
We become better able to assess the reliability of the things we think we know, and better able to search out and verify or falsify those claims that purport to be knowledge.