Lesson #1: Work is never "done"

Stop waiting  for the foreman to yank the bird and announce you're done for the day.

It took me about 5 years to figure this out: your work is never "done" in the nonprofit/ charity sector. No matter how many hours you put in, you'll never finish feeding the hungry, sheltering the poor, or saving the fish. 

The list of things you didn't do today will always be much longer than the list of things you did do. In other words, you fail someone somewhere in some way every single day.

The most successful people I know are the ones who are bothered by this - because it means they care - but still find a way to sleep at night - because it means they survive.