Debt. "What chance has made yours is not really yours." Maybe he also calls for doubt and hesitation when offered a gift because of our reciprocal nature? Whenever we get something, we feel the urge to give something back – which usually is good. But when you take it from another perspective then you can say that whenever you give, you expect to be reciprocated. Thus, accepting gifts creates a debt that ought to be paid back. Something that slows us down and puts chains on us. It's a short term gain and long term loss.