[mikestew]

why is it more complicated than buying a water bottle off Amazon or a Netflix subscription?

It's not. This is one of those "tell me what happens when you navigate to a URL" interview questions. What really happens when you order something off Amazon? Is there a float? Is there delayed settlement? Does Amazon at some point have to settle with another party? And the answer to all of those questions is "yes". We could continue to deconstruct your analogy, but I think the point is made.

Sibling comment made an analogy to buying a car. I believe if one really tore into the question, one might find that just about the only financial transaction that doesn't work with many similarities to the stock market is handing a fiver to the clerk at your local convenience store. (And someone that knows more about retail than I do can tell me how wrong I am about that.)

[maratc]

You're very much on the point, I'd just add that a fiver in a cash register is both an asset and a liability, as anyone with a gun-like object might come through the door and take it. It's only when that fiver, together with the rest of cash, is taken at the end of the day to the bank and deposited there that your $5 grocery transaction can finally be considered settled.