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.

Today, people only do a few things well.

Nowadays, people say that we have to learn as many things as much as we can and we have to be good at these things, even though we don't actually need to know how to do these things that perfectly. In my opinion, we don't need to doing many things well in order to live or survive. We don't need to spend a lot of time have to learning or studying something just to be good at it by spending a lot of time. We only need to do well in be good at our work area or our hobby.

Alternatively: 'We only need to be good at our work or our hobby.'

First of all, many people spend a lot of much time trying to be good at many things that they dont actually need to excel in. They want to be a best person in that field of that they are trying to be good at. They sometimes get stressed when they are doing that and it makes people stop doing that quit easliy. They sometimes don't sometimes learn something step by step to be best on every thing eventhough people don't expect that they would be good at specific things. (I am not sure what you are trying to say here.)  So, don't try many things above outside of your ability to save your time.

Secondly, We are humen beings and always want to be better than other people in everything anythings. Whatever people they do, they want to be a the best one. I think it is a very good attitude and positive thought to have. But However, if we try to be best at every single work or things that we do, it will be irritating to us, because people will keep asking us to help them with something that we do well. At the beginging of that time, we will feel happy about helping others. Eventually, we will feel tired if we keep doing that. Therefore, we should be good at only few things that we are working towards or that we are really like doing. All we have to do is just being good at a few things that you are supposed to be good at, such as your major or hobby.
In conclusion, we dont need to be doing many things well. We have limited time. The more things we do are doing well, the more we get stressed. It will be enough to live doing a few things well, such as your work.