The obvious irony is that the guilty party is usually the one who is most lacking. Carpe Diem suggests living a life of utmost quality, using every breath and ounce of flesh we have available for our resources. This suggests a constant vigilance or awareness of each step we take, no matter in what manner or direction. It suggests that one not miss any opportunity to reach out and touch or say what is in one's heart at any given moment. It is a positive way of being, similar to the concept of making bank deposits that only accrue interest against no withdrawals.
Some considerations are more serious in nature.
It's true, one never knows that would be the last kiss, the last time to make love, or the last time to see that smiling face. This is another argument against drawn out fights of any kind. Think it, say it, do it and be done. There are other such missed opportunities that carry regret because one did not take a certain action. An example would be similar to the one Robert Redford gave in the film, Indecent Proposal .