Defi is kind of crazy. It has three baddies you are fighting against: bad actors, bad code and yourself(bad user)

Defi is such a wild ride. Ordinarily, you would just be up against people trying to steal from you. And in Defi, these people are invisible, and most people don't even understand the processes by which you can be hacked in Defi. Perhaps the most significant is a sandwich attack, where you can initiate a swap, and a hacker can read the mempool(database that stores all transactions in-process), pre-emptively perform a swap the raises the price higher than market, your transaction then goes through and you end up swapping at above-market rates and lose money and raise the price, then they swap right after you and make huge profit being able to swap/sell at a high above-market price that happened as an outcome your transaction and make good profit.

There's also just bad code, like what happened at Sushiswap where the code was exploited to allow a bad actor to drain wallet funds. There's also purely bad code where funds are locked up, mistransferred or simply lost due to code errors with no way to get it back, like the project on ZkSync.

And then there's plain old user error of sending to a wrong address or network.

There is quite a lot you're up against in Defi. The user experience and maturity of it has a ways to go.