I once had my pocket picked. It was on a bus in Sri Lanka and I never even noticed that I had lost something. But the thief made a mistake in that he mistook a case containing keys for a wallet. When he discovered his error, he threw the case away and left the bus. When I later discovered my loss I asked the conductor if he had seen my keys and he said that he had found them and gave them back to me. So I had a lucky escape.
But pickpockets are extremely skillful and some cities (Rome, Paris, Bangkok) are notorious for being infested with them and people are urged to attach their wallets to a chain that passes over their neck and tuck it inside their shorts or blouses.
In this clip, a pickpocket shows how he can get away with it even when the victims know he is going to pick their pockets and with the cameras pointed right at him.