It's expected that you'll return items that you borrow.
Paul was using his grass trimmer on his lawn when it suddenly stopped working.
Paul wants to finish his yard work.
Paul finishes his yard work by borrowing his neighbor's grass trimmer and returns it as soon as he is done.
Paul asked his neighbor to borrow his grass trimmer to finish his yard work, but forgets to return it.
His neighbor can trim his lawn whenever he wants without having to ask Paul to get his grass trimmer back.
His neighbor has to come ask for Paul for his own grass trimmer back when he wants to trim his lawn.