Other people, it seems:
Are you selfish or generous? Or do you follow the herd, always giving whatever the majority of people deem appropriate?
Society is a mixture of these three types of character, but most of us are the last type, altering our generosity to fit the societal norm, new research has found. It suggests that governments could prompt huge swathes of the population to become more charitable simply by giving more itself or by providing other benevolent role models.
I am a little doubtful about that last sentence (remember crowding out?, and note that the policy implication comes from the journalist, not the researchers!), but here is the story from The Economist. The quotation is from the 22 January New Scientist. Here is Dan Houser’s home page. Here is one paper behind the research.
One bottom line: You are not as benevolent or generous as you think. The main reason you gave to tsunami victims is because other people did.