I'm going to put someone's stuff in the lost and found.
Why are you putting it in the lost and found?
Because I don't need this anymore and don't want to hold onto it.
It can be annoying to look after things that are not ours but we should still think before we do something. If you don't want to hold onto it, give it back to the person and tell them.
Oh, I didn't think of it like that.
If they left it with you, it is your responsibility to take care of it. Putting it in the lost and found could open up their stuff to being taken by someone else.