By the end of this you will understand what DeFi actually does, how a trade goes through with no company behind the counter, and why FTX could spend your money but a swap pool could not.
Walk into a bank and strip away the marble. It does four plain things: swaps one currency for another, lends money out, lets people borrow, and holds deposits.
Behind each of those desks sits a person. DeFi is what happens when you rebuild every desk as software and send all the people home.
Picture a vending machine on the exchange desk. It holds money, follows fixed rules, and serves anyone who walks up. It never calls in sick, never plays favorites, and cannot decide you look suspicious and say no.
That machine has a name. Code that holds funds and runs its own rules with no human in the loop is a smart contract. The whole of DeFi is a row of these machines where tellers used to sit.
You step up to the exchange machine to swap one token for another. It quotes you a price instantly. No trader, no manager, no order desk in sight.
So where did that price come from?