And it wasn't that she couldn't afford to leave more. She was simply tight. Christians, especially, should let their generosity spill over into all aspects of life, including tipping a tired waitress. It's no fun to think you've bonded beautifully with a brand new friend, only to find that the moment you turn your back, you are spoken of disrespectfully. People need to be able to trust each other in order to form an enduring alliance.
Friendship IS a two way street.
If you are repeatedly getting nothing in return for your selfless efforts, concentrate on finding people who are more appreciative of what you have to offer. We are not obligated to force ourselves endlessly upon others. Friendship is a gift. A gift is to be treasured and appreciated. When you are blessed with the type of friends who realize the value of what you have to offer, a mutual effort will be made to maintain that relationship.