Often times we take this idea to mean that all of the pleasures of the physical world will be left behind. This is meant to recallibrate our relative valuation of particular actions and remind us that what we are about to do, although it will probably be enjoyable for the next few minutes, hours, days, weeks, months, or years, is ultimately something finite, and the price is much steeper than we are willing to admit.
That is basically the pshat, the simple understanding of the metaphor: scare yourself out of the craziness you are about to involve yourself in.
I have what I think is a new and slightly different understanding of the metaphor: Even when you know you want something good, to serve HaShem through life and eventually death, what is your death ultimately going to look like?
For me the answer is that I want my death to be as meaningful as possible, please God may it be at the end of 120 years. The only way my death can be that meaningful is if i've already made my life meaningful going into it.
Right now the way I see it is, if I gave my life today, how big would the kiddush HaShem be? Only HaShem can really know that, but would it be bigger if I did just one more mitzwah? Certainly.
So, when I look at the day of my death, it isn't a sad abrupt wake-up call to remind me of how fleeting all these worldly pleasures are, it's an alarm clock reminding me I have a date with destiny and I want to have time to properly present myself.
In the end, when and how I go is up to the sole discretion of He who created me, as R' Haninah ben Teradyon said, "It is better that he who gave me life should take it from me." Yet, whether I face that end a recalcitrant child who doesn't want to go home, or a refined Tzaddik with no wish but to serve HaShem however He wills, that is (at least partly) up to me.