What is the difference between 'mediocre' and 'extremist' fields in terms of income potential?

The host distinguishes between 'mediocre' fields, where income potential is capped and growth is limited, and 'extremist' fields, where there is no ceiling on earnings. He explains that in mediocre fields, such as traditional trades, one can only earn a certain amount, while in extremist fields, like writing or entrepreneurship, there is the potential for exponential income growth. He advises focusing efforts on extremist fields to maximize financial success.