In my country to ride the bus you buy tickets in the shop. Once you get into the bus you invalidate the ticket by printing date and hour on the ticket with the device installed there.

Once in a while (once in few weeks or months depending on your luck and how much you ride) the guy shows up on your ride who checks if everyone has properly invalidated tickets. If you don't have one, you'll get a fine.

If you wish you may never buy the tickets and just pay fines when they happen. Every time you ride without the ticket you earn but you take the risk of the fine. You might argue that it's contolled risk since you estimated how often fine happens on average. But everything is awesome until one time you encounter streak of fines that eat up all your previous earnings and some future ones too.

It's the same game that those banks that invested in derivatives were playing.