You should always return someone's things.
Linda's laptop charger got frayed over time, and she had to borrow one from a friend, so she could use her computer.
Linda wants to have a laptop charger to use long term.
Linda returns her friends charger and orders a new one for herself off of the internet.
Linda keeps her friend's charger, hoping that her friend will forget and won't ask her to return it.
Linda's friend appreciates getting the charger back and tells Linda she can use it anytime she needs.
Linda's friend gets annoyed that it's taking so long to get her charger back, and she doesn't lend Linda anything else after that.