"Be the best." You hear it all the time. Constantly striving to be the best in anything that you do. But that's not realistic in a broad sense: you can't be the world's greatest chef, baseball player, parent, video game player, driver, singer, and dancer. Quite the contrary, you are constantly balancing everything you do—getting better in one area almost always requires you to not do other things and, therefore, not improve in those areas. Life is a series of tradeoffs. So what can you do? Dare to be mediocre.
Of course, "daring to be mediocre" doesn't mean to half-ass everything in your life that isn't your primary goal. Rather, it's about identifying what is "good enough" in your life. Your life goals will not be equal; if you want to be the world's greatest cellist, you may not care as much about your physical strength and so are satisfied with running two days per week to maintain your physical health. That is not going to make you look like Arnold Schwarzenegger by any means, but it is good enough for you so that you can continue to improve at playing the cello.
The most challenging area for you might be career. Everyone seems to be competing to have the best title, the most money, and the best stuff. If you look at reality TV and social media too much, you couldn't be blamed for coming to that conclusion. But the truth is that not everyone needs to be a CEO, work 100 hours per week, and never see their children just so they can make a seven-figure income and show off how successful they are. Instead, you might care more about making the most of your life by having children, pursuing hobbies, and only working the bare minimum that you need to earn the money to support the lifestyle you seek. In other words, you might "dare to be mediocre" in your job to have a great family and personal life.
Now, you don't have to actually see what you're striving for as mediocrity—that's just a funny, memorable way to describe the idea. In reality, you're simply identifying what you want in life and what you need to do to achieve those goals, which will lead you to prioritize which areas are most important and how much time you can allocate to each. You can try your best in everything you do, but you also realize when something you've done is "good enough" so that you can move on to the next area. It's all about focusing most where you need to and accepting the best you can do in the time you had elsewhere.
There is a term for this in psychology called "satisficing" (vs. "maximizing"). Satisficing is when you look for the "good enough" solution and stop vs. someone who will continue searching for the best solution to maximize the value of their efforts. There is a lot of research on the topic to evaluate the affect of going for the best vs. "good enough" on the amount of happiness or regret these people might find as a result. The researchers concluded that it's difficult to see objectively which approach was superior because there are situations where you might be better off taking one approach vs. the other. That's exactly how it works in life: there are areas of your life where you just want to solve a problem or complete a task and don't need the best materials, approach, or solution because it would require more time and effort than you're willing to invest. So, you just find something that meets the need and buy/do it.
This is the exact reason why you should find what matters to you and focus a disproportionate amount of time on it ("maximizing") and look for areas where you can do just what you need to do to satisfy the need elsewhere ("satisficing"). Take this approach, and you'll find the best way to allocate your time and effort in life so that it's as rewarding as possible. You may have to learn to accept that others might judge you for your life choices—it's much easier than fighting a life-long war to get people to stop judging you, but you're welcome to try that if it makes you feel better—but you will ultimately only have yourself to answer to at the end of the day (and at the end of your life).