That means not putting yourself out just to win friends but doing what makes you happy.
I have had similar experiences, not that I considered myself exploited, though others tell me I was. Quite recently in fact.
I remember it was my choice to be generous and if they were just using me then they have a problem not me. Naturally I cease being there for them since it doesn't serve anyone for me to allow myself to be used. It's a matter testing the water since we don't know how comfortable we will be in the friendship. Yes there will be people who just use others generosity but we all eventually find our real friends.
In being generous and doing small favours I'm being kind to myself because that's the kind of person I like being. There will be times my generosity lands with someone who might not have earned or deserved it. Then again who's to say? In the scheme of things it's all good. If I don't feel right about it I stop. It's a friendship or relationship I sort but wasn't meant to be.
So yes it does work with large numbers. You only do it as long as you're happy doing it.