The comment said "one of the most reliable ways", not the only reliable way. Furthermore the two are not mutually exclusive. I worked at Microsoft and Google before starting my own company, mostly as a way to pay off student debt. A few of my co-workers at Google also left to start their own companies as well. There's no reason why you can't put in a couple of years at a large company to make some early cash, then leave to start your own company.
If it fails you can almost certainly go back to working at a big company and heck even try again later on in life.
But it's not reliable at all. Particularly when you consider the longer and longer time to exit, the greater dilution due to those huge late rounds, the fact that you get hit with the tax burden when you exercise (which can easily be a decade before that stock is liquid), the fact that the late rounds have significantly raised the bar on what a 'successful exit' is.
Now that startups tend to stay private so long, the value of employee equity has absolutely tanked.
If it fails you can almost certainly go back to working at a big company and heck even try again later on in life.