There's a technical solution concept in game theory that mirrors Diane's reasoning here. I wish I could remember the name of the solution concept offhand, but the idea is that, even though your own decision won't affect the decision anyone else makes, you still make the "altruistic" decision, reasoning that the other people involved will use the same reasoning and come to the same conclusion.<p>The paradox, of course, is that, having come to that conclusion, you could just choose to make the "non-altruistic" decision. Everyone else has already decided what they're going to do, so you won't change that. Except the solution concept stipulates that they reason exactly as you do, so if you make this decision, so will they.