Focus is a simple concept and a very challenging practice.
Focus is understanding what is important and what not in your life, what you want to achieve and what is your end game. Where do you want to get before your time is over?
Focus is making short and medium term decisions about what to commit to and what to say no to. Is that next thing that looks so shiny and everybody is using going to help you get where you want to get before your time is over?
And focus is also a minute after minute choice on what to respond to, what has the power to distract you, to push you through a black hole of wasted time and energies. Should I keep notifications on or off? Shoul I keep the mail client always running in the background? Is it ok to be active in the official work chat? How do I react next time someone stops at my desk/office for a chat?