At the beginning of 2017, I read the book "Essentialism" by Greg McKeown. The book covers, in-depth, the idea of focusing on only the most-essential tasks. In order to do this, you need to prioritize your time; you need to say "No."
If you don't learn to say "no" to what you don't want to do — and "yes" to the things you really want to do — then someone else will dictate your time and priorities. Your email inbox will fill up with requests; your chat application will shout at you; your calendar will be filled with meetings and events. Other people will control your time and attention.
Time is our most valuable resource. So why would we give it away?
Saying "No" to something is saying "Yes" to something else. Jason Fried
If we say "no" to something — or, more importantly, someone — we're not telling them we don't care about them. We're saying "yes" to what really matters to us. And once we get to that place, it's freeing, like the feeling of closing your eyes and taking a deep breath.
The next time someone asks you to do something — or invites you to an event (party, meeting, etc.) you don't have the time for — say "no".
Because "No." by itself is blunt (and potentially harsh), it's often helpful to provide transparency into your reasoning.
I'm sorry. I have existing commitments and objectives I'm focused on, so I won't have time to be in the meeting you invited me to.
If you don't prioritize your time, someone else will.