It's rude to steal something that another person is using.
George's teacher just gave the entire class a writing assignment when he realizes he left his pencils at home.
George wants a writing utensil.
George asks his neighbor if he can borrow a pencil for the day.
George snags a pencil off of his neighbors desk when they aren't looking.
The student next to George gives him a pencil, and they start talking end up becoming friends.
Somebody else see's George steal the pencil, and tells the teacher causing George to get sent to the principals office.