I shall pass this way but once. Therefore, any good that I can do or any kindness that I can show, let me do it now, for I shall not pass this way again.
Regardless whether one believes in reincarnation or not, it remains an undeniable truth. We pass but once at any given moment. Every day, every hour, every person I encounter at a moment of that day, is a once in a lifetime. It will not occur again. Ever.