Here's a thought experiment: imagine you're walking down the street on your way to the bus stop or the library or to pick up lunch and you notice a series of cars parked at expired meters. If you, as an ordinary citizen, could give these drivers a parking ticket, would you do it?

(from Wikipedia)

I think the overwhelming response to this question would be no. In fact, it's been documented on several episodes of A&E's Parking Wars that random pedestrians (some of whom admit that they don't even own a car) are sometimes the most hostile toward the meter maids writing the tickets.

Now consider this: you're in your car on the way to the bank to make a quick deposit. There isn't anywhere to park near the bank, and there are a series of cars sitting right in front of the bank with expired meters flashing. On your way into the bank, would you give these cars a ticket?

I'd hypotehsize that people would be more likely to give a parking ticket in the second scenario, because, after all, it directly and negatively impacted their own ability to park. It would "teach the jerks a lesson" and improve the odds that the next time around, the coveted space in front of the bank would be available. What if the citizen ticket-writer even got a cut of the proceeds, say 25%? We could eliminate illegal parking overnight!

Of course, this is just a thought experiment. What happens in reality is much different. Seeing there is no place to park despite the expired meters, the typical driver double-parks to run into the bank. Maybe he gets away with it 9 out of 10 times, but the one time that he gets busted, he curses the meter maids, curses the city, and generally gets angry at everyone except the two people at fault (himself and the other illegal parker). Then, from that point forward, this person is psychologically conditioned to hate parking enforement agents. They're the 'bad guys' - the ones who give him tickets at inconvenient times. So when he sees a car getting a ticket, he sympathizes.

Altruism, it seems, might actually just be a symptom of helplessness.