It's wrong to dirty up other people's things.
Steven's car is at the mechanic's getting fixed, so his friend Rocco has lent him one of his cars to drive around for the week.
Steven wants to go fishing.
After a day of fishing, Steven changes into clean clothes and puts his fish in a secure cooler before getting into Rocco's car to drive home.
Steven spends a day fishing before returning to Rocco's car in muddy boots and spilling a bucket of fish all over the back seat.
Rocco's car is returned in perfect condition.
Rocco is left to clean up the mess when Steven returns the car and loses his trust in him forever.