It is said that if you would have peace of mind, busy yourself with little. But wouldn't a better saying be do what you must and as required of a rational being created for public life? For this brings not only the peace of mind of doing few things, but the greatest peace of doing them well. Since the vast majority of our words and actions are unnecessary, corralling them will create an abundance of leisure and tranquility. As a result, we shouldn't forget at each moment to ask, is this one of the unnecessary things? But we must corral not only unnecessary actions but unnecessary thoughts too, so needless acts don't tag along after them.
-- Marcus Aurelius, Meditations, 4.24
"What vanity obligates us to do, what greed signs us up for, what ill discipline adds to our plate, what a lack of courage prevents us from saying no to - all of these we must cut, cut, cut"
* Source: The Daily Stoic by Ryan Holiday and Stephen Hanselman