Saying "No":

Cal Newport:

"The question left unexamined in my essay is what it would look like if you rejected this rule. What if, for example, you aimed to work 20% less than you had time to reasonably handle? If you have a relatively autonomous, entrepreneurial type job, this would mean saying “no” to more things. It would also mean, on the daily scale, being more willing to end early, or take an afternoon off to go do something unrelated, or extend lunch to read a frivolous book."