It is 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 that we will begin to live each day to the fullest, as if it were the only one we had.

The quotation frames mortality-awareness as the catalyst for authentic living. By insisting that we both “know” and “understand” our limited time—and that the endpoint is unknowable—it links existential uncertainty to ethical urgency: procrastination and complacency become irrational when tomorrow is not guaranteed. The line echoes Kübler-Ross’s broader cultural impact as a clinician and writer who brought frank discussion of death, dying, and grief into public conversation. Read this way, the quote is less a sentimental “carpe diem” slogan than a practical prescription: accepting finitude can sharpen attention, reorder priorities, and encourage fuller presence in ordinary days.