Put it this way, before 1980, sure. But over the last 30 or so years it's been a different ballgame.
There were 100 baggers available by selling at the top of the internet bubble. Or buying MDVN 10 years ago or tucking away some AAPL in the dark days. And these opportunities aren't dying out; for example, the same scenario is playing again right now in immuno/gene therapy.
Expand that out to real estate, Forex, domain names or just about any other investment/speculative vehicle over that time and you're talking a massive # of individual opportunities that yielded multi-fold returns. Returns that could be parlayed into further opportunities.
So imo it's not unreasonable for someone to turn $1m into $30m over a 20 year span even with average discipline, intelligence and luck.