Why does seriously wanting to know something commit you to the idea that truth is not merely relative?

Because a knowledge-claim asserts validity for everyone, not just for you — and a "truth" that holds only for me is just an opinion wearing a disguise.

The material (citing Ostritsch) draws a line between mere opinion and a knowledge-claim. When you say "I know X," you're not just reporting your private state — you're claiming X is valid for others too, that they ought to accept it as well. Opinion makes no such demand.

That's why genuinely wanting to know something pushes you toward a non-relative notion of truth: if you really seek to know, you must believe there's a truth that isn't simply "true for me." A truth that's relative to each person isn't truth at all in this sense — it's just an opinion.

This matters for the whole topic: bullshit, "alternative facts," and "my truth" all chip away at the shared, binding notion of truth that knowledge actually requires. Critical handling of information assumes the distinction between true and false is real and worth defending.

Tip: Test a claim by asking: am I asserting this should bind everyone, or just expressing how it seems to me? Conflating the two is where "my truth" quietly replaces "the truth."