Giving, whether money, time, or attention, is consistently linked in wellbeing research to a modest but reliable boost in the giver's own sense of satisfaction, often rivalling or exceeding the boost that comes from spending the same resource on oneself. The effect holds across a surprisingly wide range of cultures and circumstances.
Part of the explanation seems to be a sense of connection: giving usually involves another person, and that human contact, even briefly, appears to matter more to wellbeing than the material value of whatever was given. A small gift handed over in person tends to outperform a larger one sent anonymously.
The link also appears to work best when giving feels chosen rather than obligatory. Generosity given freely, without pressure or expectation of anything in return, seems to carry more of the wellbeing benefit than the same act performed reluctantly or purely out of social duty and obligation.