Generosity has a threshold. Below it, giving costs the giver something real — the ten pounds handed to a brother has to come from somewhere before Friday, and both of them know it.
Above that threshold, giving becomes nearly frictionless, and the odd thing is that it doesn't necessarily feel better. It just stops being an event.
People who give most freely aren't reliably the ones with most. But being drenched, if it comes, removes one specific pain: the small arithmetic that runs between hearing somebody needs help and saying yes.