In short, you want skills that are leveraged.
Naval Ravikant has a great piece talking about leverage which you can read more on here
Naval explains that historically we have only really had two types of leverage:
Money leverage - amplify results by using money
Labor leverage - amplify results by using people
But money is hard to come by, and labor requires you to pay for wages or people being willing enough to follow you (like a popular politician).
Naval explains however, that there are two new forms of leverage:
Code leverage - write one line of code and have an army of robots work for you
Media leverage - make one video and be seen by millions of people
Code and media leverage are especially powerful because they are free, and are permissionless (unlike a banker to approve your loan, no one stops you from learning to code).
Anyone can learn to code, and anyone made youtube videos and reach millions of people.
Conor McGregor has built skills in two areas of leverage: money (using his whisky business to grow his capital) and media (using his showmanship to increase his audience reach and influence). Both are supported by a fundamental core strength, fighting.
In 2021, the best skills for you to invest in are leveraged ones.
Core skill + leveraged skill + leveraged skill = unstoppable force