thanks to cashewman
The tragedy of the commons
The tragedy of the commons is an idea created by ecologist Garrett Hardin. It describes a situation in which "multiple individuals, acting independently, and solely and rationally consulting their own self-interest, will ultimately deplete a shared limited resource (the commons) even when it is clear that it is not in anyone's long-term interest for this to happen." In other words, this happens when what's best for a group of people conflicts with what's best for individuals.
Cows in a piece of land
Let's try to understand what this means. (thanks Wikipedia!) Imagine a group of herders sharing a big common parcel of land, on which they are each entitled to let their cows graze. It is in each herder's interest to put the next (and succeeding) cows he acquires onto the land, even if the carrying capacity of the common is exceeded and it is temporarily or permanently damaged for all as a result. The rationale is: The herder receives all of the benefits from an additional cow, while the damage to the common is shared by the entire group. Additionally, the damage to the common is too small to be spotted at first. If all herders make this individually rational economic decision, the common will be depleted or even destroyed to the detriment of all.
Note that you don't even need to be greedy and put in many cows. Even just one cow will degrade the common, but at a slower rate. This is the real tragedy.
Translating to modern times
This translates very well in modern times because we still have commons, and many more people than in medieval times. Our capacity for raping the environment has also increased.
So in the example above, if you would take air as your commons, and cars as the cows, the situation is the same. We know cars will degrade the air around us, but the damage is too small to be felt, and the damage is shared by everyone. The benefits to the individual would outweigh the damages, given the individual is comfortable financially. So it's in everyone's best interest to drive cars everyday and/or get more cars. But, there will come a time when this environment can no longer bear the damages and shut down.
This is true not just for cars. Take littering for example. When you litter, each individual instance brings too little damage to the overall environment, so everyone does it. But at the end of the day, we see that the floods are caused in part by blocked drainage due to the combined effect of everyone littering.
I just hope this concept was taught in university. I think one of the impacts if this was widely propagated is a decrease in consumerism, and our economy in its current framework would suffer.
What does it mean to me?
What this means to me is that I won't be having a car for quite some time. There will come a time though when I can no longer make the sacrifices. And it's sad.