It’s only when we truly know and understand that we have a limited time on earth - and that we have no way of knowing when our time is up, we will then begin to live each day to the fullest, as if it was the only one we had.

The saying frames mortality-awareness as a catalyst for authentic living. By stressing both the finitude of life and the uncertainty of its endpoint, it argues that procrastination and complacency are sustained by the illusion of abundant time. Once that illusion is punctured, everyday choices gain urgency: attention shifts from abstract future plans to present commitments, relationships, and meaningful work. The sentiment aligns with Kübler-Ross’s broader cultural association with end-of-life reflection—how confronting death can clarify values—though the wording here reads like a modern motivational paraphrase rather than a tightly sourced line from her clinical writing.