The situation:

• You take the bus to school
• You have a bus pass sticker on your student ID
• As the bus pulls up, you realize that you left your student ID in your other jacket
• You tell the driver, and their stoney face indicates you're going to need to pay the $1.75
• You reach in to your pocket, dig through your backpack, and find that you only have $1.50 (and a couple twenties, but really).
• You tell the driver you only have $1.50. What should you do?
• The driver says okay, but pay the quarter the next time.
• You say okay.

Okay, now flash-forward to tomorrow, when I step on to the bus, armed with my ID with bus sticker: What's my obligation? Should I pay the quarter? Am I really owed a $1.50 that I'll never get back? Do I just forget it and move on?

It's the little questions that can be fun.