Diagram attached. Excuse my artwork.
I was in a busy supermarket car park on Friday. I don't normally shop there and didn't realise that the school over the road kicks out early on Fridays, so the car park was rammed with parents picking up their children when I was leaving. I was parked at the far end of the car park. I queued to exit, let in a car queuing in the next lane along, but not the cars in all the lanes after that. It took me 25 minutes to get out of the carpark.
The drivers of the cars I didn't let out seemed really annoyed and were glaring/beeping. In my mind, I let out one car and so had done my bit. If I let out one car from every lane, and the cars I let in also let in one car from every lane, that would have added about 10 cars in front of my original position. Surely, the car I let in just lets a car in from the next lane, and so on?