I originally read the first quote below in Getting Things Done by David Allen. I really feel better about some of my weekends after discovering the second quote.
Besides the noble art of getting things done, there is the noble art of leaving things undone. The wisdom of life consists in the elimination of non-essentials.
If you can spend a perfectly useless afternoon in a perfectly useless manner, you have learned how to live.
Society can exist only on the basis that there is some amount of polished lying and that no one says exactly what he thinks.