How simple can a microprocessor-based system actually be?

A Microprocessor must be contain a microprocessor otherwise it is simply another electronic circuit. A microprocessor must be programmed. This means that it must be provided with a series of instructions to be followed. However we program the microprocessor, the result is a series of binary numbers that represent the simple step by step instructions to be followed. These instructions must be stored in some memory. But do the instructions have to be stored in RAM or ROM. Now Question is Where it store ? It must be in ROM. Remember that RAM will hold random data when first switched on and if our microprocessor was controlling the operation of a dynamite factory, the last thing that we would want is for it to start following random instructions at the rate of a million a second.