Today, people only do a few things well.

First of all, many people spend too much time trying to be good at many things that they don't actually need to excel in. They want to be  the best person in that field. They sometimes get stressed in the field they are working or studying in and it can make them quit or stop working. They sometimes don't want to learn something step by step or be best at everything, even though people don't expect that they would be good at one specific thing. So, they don't try many things above their ability to save time.

Secondly, We are human beings and always want to be better than other people in many things. Whatever people do, they want to be the best one. I think it is a very good attitude and positive thought to have,  but  if we try to be the best at everything that we do, it will irritate us, because people will keep asking us to help them with something that we do well in. At the beginning, we will feel happy about helping others. We will eventually  feel tired if we keep doing that. Therefore, we should be good at a few things or choose something we enjoy doing.OR this -> All we have to do is be good at few things that we think we would excel in, such as our major or hobby. 
In conclusion, we don't need to do many things well. We have limited time. Therefore, the more things we do well, the more we get stressed. It will be enough to live doing a few things well, such as your work.