Imagine a sausage factory – the luckiest, most profitable sausage factory in the world. Its machines crank out their sausages, and lorries carry them to supermarkets. So far, so normal.
But this particular factory makes as many sausages as the management and staff choose. If they feel like taking the day off, the lorries and shelves stay empty. If they want to go a bit wild, they sometimes make so many sausages that there aren't enough lorries to take them away. Or they carry on cranking out sausages even if the shelves are already full.