This is a commonly repeated trope, I guess it's to inoculate people from being "suckered in", but it hasn't been true from what I've seen, having lots of friends involved startups. Even "failing" startups frequently get acquihired for non-trivial amounts per person, and since the point of that is to get the people, those amounts typically go to retaining the people. And many of the people I've known have done really well by employee equity, a couple with multiple 7 figure payoffs, some with instant retirement amounts, a couple with serious maybe-I-buy-a-jet megawealth.

It's not guaranteed like a FAANG salary (which actually isn't completely, the past few years have seen great stock appreciation), usually it takes a few rolls of the dice, but it's just not accurate to describe it as a definite 0. Startup selection ability pays a serious role here, I've seen people whose picks I shake my head at consistently, and some people who can home in on successful ones like heatseeking missiles. If you're the type to take the story of a business person about lofty valuations and prospects at face value, though, you're probably going to have a bad time and end up bitter and talking about how bad a deal startups are on the internet.