Why would anyone bother making door-keys shrink?’ said George.‘Just Muggle-baiting,’ sighed Mr Weasley. ‘Sell them a key that keeps shrinking to nothing so they can never find it when they need it ... Of course, it’s very hard to convict anyone because no Muggle would admit their key keeps shrinking – they’ll insist they just keep losing it. Bless them, they’ll go to any lengths to ignore magic, even if it’s staring them in the face ...
J.K. Rowling
harry-potter, magic