You open a yield comparison tool, see a long list of Polygon pools, and immediately spot one offering triple-digit APY. Your next thought is probably: "Why would anyone pick the boring 2% option?" That instinct is completely understandable — and it's also the most common way beginners get hurt in DeFi.
What the Numbers Are Actually Telling You
Two figures appear next to almost every pool: APY (Annual Percentage Yield — the annualised return if conditions stayed constant) and TVL (Total Value Locked — the total amount of money currently sitting in that pool).
Take a concrete example from Polygon's current data. WBTC — a tokenised version of Bitcoin that runs on Ethereum-compatible blockchains — is sitting in an Aave v3 pool with roughly $49 million in TVL. Aave v3 is one of the most widely audited lending protocols in DeFi. A pool that size has been scrutinised by a lot of eyes, which matters when you're thinking about smart-contract risk (the possibility that a bug in the code could drain funds).
The APY on that pool sits at effectively zero right now. That might look unappealing, but it tells you something real: demand to borrow WBTC on Polygon is low at the moment. The yield is honest. It isn't being propped up by reward-token emissions — temporary bonus tokens that protocols hand out to attract deposits and can disappear overnight.
The Trade-Off Nobody Puts in the Headline
Higher APY almost always means one or more of these things: the pool is smaller and less battle-tested, the rewards come from token emissions rather than genuine fees, or the underlying asset carries more volatility or depeg risk (the chance a token loses its intended value). None of that makes a high-APY pool automatically bad — but it does mean the comparison work falls on you.
A useful habit: sort by TVL first, not APY. Larger pools have generally survived longer and attracted more independent security review. Then look at what's generating the yield — fees, lending interest, or reward tokens. The comparison table lets you filter Polygon pools side by side so you can see both figures at once.
One question worth asking before you deposit anything: if the reward tokens stopped tomorrow, would this pool still offer a return worth the risk?