This is from How to Fail at Everything and Still Win Big by Scott Adams, creator of Dilbert

The Selfishness Illusion
During your journey to success you will find yourself continually trying to balance your own needs with the needs of others. You will always wonder if you are being too selfish or not selfish enough.

For starters, when it comes to the topic of generosity, there are three kinds of people in the world:
1. Selfish
2. Stupid
3. Burden on others

That’s the entire list. Your best option is to be selfish, because being stupid or a burden on society won’t help anyone. Society hopes you will handle your selfishness with some grace and compassion. If you do selfishness right, you automatically become a net benefit to society. Selfish successful people don't cause worry and stress for those who care about them. As a selfish successful person, you can be a role model for others. Selfish successful people can be fun company if they've squirreled away all they need and have no complaints to voice.
[...]
By "selfishness" I don't mean the kind where you grab the last doughnut so you're coworker doesn't get it. That wouldn't be enlightened selfishness because that source of pettiness can bite you in the ass later. And it might rob you of some energy if you feel guilty about it or you get caught.

The most important form of selfishness involves spending time on your fitness, eating right, pursuing your career, and still spending quality time with you family and friends. If you neglect your health or your career, you slip into the second category--stupid--which is a short slide to becoming a burden on society.

I blame society for the sad sate of adult fitness in the Western world. We're raised to believe that giving of ourselves in noble and good. If you're religious, you might have twice as much pressure to be unselfish. All our lives we're told it's better to give than to receive.