For Chen Cheng, the "standing on one's own feet at the age of thirty" refers to the interest rate.

From 3,000, 100,000, 1 million, 10 million, to hundreds of millions...

More and more principal, a steady stream of interest.

The way money makes money and interest makes compound interest makes Chen Cheng sigh:

I can never spend all this money! I can never spend all of it! I can never spend all of it in my lifetime!