One framing I keep coming back to is this: in DeFi, if you cannot name the source of your yield, you are probably the yield. What is happening: DeFi yields come from lending spreads, trading fees, protocol emissions or risk premiums. Each source has a different sustainability profile. Why it matters: That distinction is crucial because emission-driven yields can disappear overnight, while fee-driven yields tend to be more durable. In practice: A lending protocol paying 20% APY through token emissions will see yields collapse once emissions slow. A protocol earning 4% from real lending demand has a sustainable model. Watch for: The mistake is chasing APY without decomposing where the yield originates and how long the source can persist. Useful lens: A useful review question is which funding, incentive or cash-flow channel is actually doing the work. The point is not to memorize the label. The point is to know what variable is actually doing the work.