A comic character called "Hungry Horace" had recurring nightmares of being marooned on a desert island, a crate washing up on the shore, and it being full of tinned food he was unable to open. A psychiatrist suggested he go to sleep holding a tin-opener: this should fix the object in his mind and he'd have it with him in his dream. It worked, after a fashion. In his dream he was sitting on the shore of his desert island, tin-opener in hand, eagerly waiting for the crate to appear. But this time the crate was full of tin-openers.