Look at the money in your bank account. You think of it as yours, but in practice three parties decide what happens to it: the central bank that issues it, the commercial bank that holds it, and the payment networks that move it.
Someone decides how much exists
Modern currencies have no fixed supply. A central bank can create more whenever it judges it necessary. Each new unit makes the existing ones worth a little less, which is why prices rise over time. Since 1913, the US dollar has lost more than 95% of its purchasing power.
In some countries this happens fast. In Zimbabwe in 2008 and in Venezuela in the 2010s, prices doubled within weeks or days, and a lifetime of savings disappeared.
Someone decides whether you can pay
Every card payment or transfer is a request. A bank can delay it, refuse it, or freeze the account behind it. Most of the time this never happens to you, but you are relying on permission all the same.
Someone takes a cut at every hop
Sending money abroad still takes days and passes through several intermediaries, each taking a fee. For the hundreds of millions of people who send money home to their families, those fees add up to tens of billions of dollars a year.