There is only one path to happiness, and that is in giving up all outside of your sphere of choice

From The Daily Stoic by Ryan Holiday and Stephen Hanselman. 

Keep this thought at the ready at daybreak, and through the day and night—there is only one path to happiness, and that is in giving up all outside of your sphere of choice, regarding nothing else as your possession, surrendering all else to God and Fortune.

—EPICTETUS, DISCOURSES, 4.4.39