That's not actually true. If everyone spends at once, the economy can overheat, creating bubbles and uncontrolled inflation. If everyone saves, the economy can

That's not actually true. If everyone spends at once, the economy can overheat, creating bubbles and uncontrolled inflation. If everyone saves, the economy can contract and we fall into a depression. The federal reserve uses interest rates and other tricks to try to find the (moving) sweet spot where the economy grows without a significant risk of a recession. The performance of the fed and economic policies are debatable, but the principle is sound.