This means that if you focus on becoming an expert in one subject, you are going to be successful at it.
But if you choose to be good in a hundred things, well, you may end up becoming a Jack of all trades but master of none.
But if you are just starting out or you do indeed have more than one interest, then go ahead and and experiment with them.
However, it is also important for you to be able to identify the one that you are going to prioritize the most. That should get most of focus.
Most people remain average because they don’t have a focus. They don’t set any goals. When people don’t have goals, they will expend a lot of energy on many things which none of them matters.