This is partly getting into questions about whether “pure” altruism is even possible, e.g., is an anonymous donation truly selfless if you do it because it makes you feel good.

But in the example above it’s entirely possible that you helped someone out with no expectation of being paid back. Let’s say you’re rich and the person you helped is a chronic drug addict. You have no expectation of every needing help and no expectation that the person you helped will ever be in a position to help you.

Let’s say I give a homeless person a dollar. He turns around and uses that dollar to buy a lottery ticket and wins 100 million dollars. Years later, I’m homeless and the former homeless guy walks past me and gives me a lecture about how I should have put conditions on my donation.

In that situation there was no reasonable expectation for anything except as you said maybe good will. But of course open source developers also expect good will.