It's impossible for smart contracts that are properly coded to enable anyone to pull the funds out. Nothing is 100% guaranteed but protocols like Uniswap have been around for years, their contracts have had many professional audits, and the reward for breaking them is billions of dollars, so the odds of a bug in an Uniswap pool is very low. Other protocols pay incentives to LP the Uniswap pools. Where you expect the failure to come is perplexing, but yes you know more than me.
What I'm describing is, literally, just what has happened with Luna and a lot of other yield-farming centric tokens that pay these outlandish "interest rates". Those "interest" payments are being extracted from future losses.
By the way, the point defi enthusiasts make about how that's just the same way interest in the "legacy" financial system works already is also true. The only difference is that the existing financial system takes its current interest payments out of future growth in real resources and productivity. And this is why double digit interest rates are extremely rare; because that rate of real growth is difficult or impossible to sustain for long.
But thus far, defi remains a closed purely financial loop, without creating any real non-financial growth, so it's all zero sum, just pitting current speculators against future ones.
Failure comes from the fact that the people don't give a flying fruit about some random tokens.
You can't pay the rent or utilities with them, you can't pay with them at the store or anywhere else.
Meaning unless you can convert your random tokens - that are not accepted almost anywhere in the real world - to good old USD/fiat, you virtually have nothing.
That's the failure, smart contracts do not ensure you get real USD dollars out off the system, the ones normal people accept as legal tender.
