If I had to teach this in one paragraph, I would start here: small recurring costs matter because compounding also works against you. Core idea: Investors usually notice big drawdowns quickly. Fee drag is quieter, but it compounds for much longer. Why it matters: That is why cost discipline is not cosmetic. It is part of return discipline. In real life: A strategy that beats by a little before fees can become mediocre after years of friction. Common slip: The mistake is comparing products only on recent return and ignoring what must be paid every year to keep them. Try this: Explain in one sentence what problem this idea solves and what problem it does not solve. The point is not to memorize the label. The point is to know what variable is actually doing the work.