I feel 5M is TT big shots consensus. At a more modest 5% return, 5M secures 250K a year, or a little over 20K a month. With tax benefits in long-term investing, it can replace two decent W2s without the need to touch the principal. Throwing in another 2K/person from SSI, you can live decently. Also with that much assets, your time is better spent trying to identify a higher return opportunity on your investible capital, rather than working for others.
1M cannot cut it. If you suffer a 30% loss in a bad year for stock market, but have to take out money to support daily expenses, then you might not have enough asset to participate fully in a rebound.
Granted 5M is still a lofty goal for those of us small fish who started with empty hands 10-15 years ago in this country.