Imagine your life as gas stove. On that stove are four burners. Each of those burners represents one major area of your life: family, friends, health, and work.
Here's the catch: there's not enough gas to be able to run all of those burners at 100% at the same time. How much gas should you put into each burner?
This is the Four Burners Theory.
The Four Burners Theory states that in order to be successful in one area, we need to turn off one other burner (or at least significantly reduce the gas going to it), and to be really successful in one area, two other burners need to be turned off.
For me, it also reminds me that saying "yes" to one thing must mean that I am saying "no" to something else.
By saying "yes" to having a late night out with friends, I am saying "no" to sleep. By saying "yes" to working overtime for more money and work experience, I am saying "no" to social time. By saying "yes" to working on a side project, I am saying "no" to spending time outside relaxing.
Ultimately, the answer to the Four Burners Theory will vary wildly depending from person to person depending on what their life situation is. If you're a workaholic like me, then chances are your work burner is turned to 100%, and some of that gas should probably be sent elsewhere. The answer can and should also change over the course of your life. Work may be a priority when you're young, but that may be replaced by family as you age.
There is no right or wrong answer. It comes down to where your values lie and what you want in life.