I'm not taking that to mean quit your job and use that money to start a business or whatnot. I'm operating from the premise that "retiring" means quitting and no longer earning a living other than what that 2M can generate on its own.

A safe withdrawal rate is assumed to be 4%, which means 80K in this case. For someone in their 30s, they'll have to pay family expenses, college education, the full cost of health insurance, etc., out of that 80K amount, and do so over a 50-60 year period of time. That long of a horizon has some serious chances at a major economic disruption, at which point you're in trouble.

If you had 2M in a 401K, and left it untouched for 5-10 more years while you kept working, you'd be in much better shape.