Which might mean: By declining to do favors/tasks for people, you may feel like a selfish person, but limiting what work you take on you will reduce your stress, increase the quality of your work, and and increase your status. Plus you don't feel used or resent being helpful.
A good strategy could be to decline first, check schedules, then accept if possible: "I may be able to do that, but let me check my schedule first." Good for many situations.
It's a very generic P/S/A , amenable to being understood in a multitude of ways :-)
Though my personal interpretation tends towards the resistance to conformity pressure (aka "going with the crowd") and/or defiance of authority.
P/S/A: There are single sentences which can create life-changing amounts of difference.