How is $100/month Profit Good?

[Dan Brindley]

I'm totally new to Real Estate Investing. But after reading so many times that $100 a month profit is the goal, I'm left wondering how can this be good? By my estimation I'd need 40-50 houses to make a decent living. I know I'm probably totally missing something, so can someone explain this to me. And how can someone get to own that many homes? And how long would this take? Just keep refinancing the previous loan? I would lose my head trying to keep track of that many homes even with a property management company!