What is the Spartan rule?

Could you please elaborate on the Spartan rule? I'm intrigued to know how it applies to the world of finance and cryptocurrency. Is it a strict set of guidelines that governs investments, or is it a more metaphorical approach to managing one's finances? How does it differ from other strategies or rules that are commonly employed in this field? And what makes it particularly relevant or beneficial in the ever-evolving landscape of cryptocurrency and finance?