for the rest of his/her life.. well he/she can do something to earn money or grow food by herself. It's not like we are supposed to support them forever. Of course they need a lot more help than a few grains of rice but if I just spent a few minutes of my time and that leads to some kid getting 400 grains of rice (thats about 100g of rice) then I feel that I've done my share.
Well, I realize that 4000 grains of rice won't end world hunger. I know it'll only help out to an extent that's practically invisible. But if it feeds anyone, even if just one person, that's one meal that they wouldn't have gotten otherwise. And I didn't even really have to do anything for it, I just sat down at my computer for 20 minutes and clicked away. Not only does it benefit others physically, it benefits me mentally.