There is no safe way to get rich.
Proof: There are still poor people.
How is that a proof?
If there was a simple, safe and legal way to get rich, a lot of people (= all those who know about it) would be rich. That would leave the rest (= those who don’t know) poor. But the poor would be wondering: Why am I poor?
And a some of them would eventually learn about this simple, safe and legal way to get rich and become rich, too. So over time, the number of poor people would inevitably shrink. Since it’s a safe way, the rich would stay rich. Even if they lost some money, they would just apply the scheme again to make up for the losses.
That means after a certain time, there couldn’t be any poor people left.