What is within your sphere of influence and what is not?
When you only concentrate on things which are within your control, you have to keep tabs on less stuff. You can focus your mind on the things which you do have control over and can improve upon.
This sounds very easy, but there are some minor complications. For example, it will change your interactions with others. Most people do not even think about their sphere of influence, leaving them at the mercy of what ever their impulses tell them to care about.
The weather, how you favorite sports team is doing or why Trump has said what he did last night will not influence you anymore. Because you have no measure of influence on these things.
This stoic approach helps you cut a lot of excess from your life. Leaving with a leaner set of tasks and objectives which you can actually achieve.