Taking off from a dream in which the penis was represented by a faucet, Hall suggests that one reason why a symbol rather than the actual object is used in the dream is that the dreamer is dissatisfied with the object and creates a better one. The dreamer in the example cited wished for a penis he could turn on and off as easily as a faucet. Conversely, in Hall's opinion, the inventor of the faucet was acting out his fantasy of a penis which could be turned on and off at will. Inventions in general must be based on dissatisfaction with what exists. Progressively more elaborate inventions, for example, from automobile to aeroplane to rocket, are motivated by unsatisfied infantile wishes.