"Nothing's sad until it's over."
- The Doctor

That's strangely motivating. Think of it like a song or a book or a movie or your favorite show. It's rife with happiness, laughter, tears, and serenity. It's only sad when it's over. It's sad when we can't hear it, see it, or watch it. The same is true with life. It's only sad when we can no longer live it. 

The other parallel is that the sadness is not our own. It falls to others; much like the sadness of the end of a story in a book, movie, or show is not the sadness of the characters within it, but yours.

We wish that our favorite characters and stories could have kept on. We wish that more to the story would unfold. Instead, we get left with what-ifs and fantasies of what comes next. 

The same thing happens to those who love us, when we are gone. The shorter our own story, the more they are left to imagine the what-ifs. If we cut our own story short, by our own hands, those what-ifs take dark, dark turns. They eat at the readers and watchers of our lives, leaving them with a sadness that only remains dark. 

The best thing we can do is live our stories out until there is no more story to tell. The sadness will fall upon those we leave behind, but it will be a sadness that sparks imagination, excitement, and joy. That, THAT, is the purpose of it all: to leave a story worth continuing in "fan fiction." THAT is why I'm thankful to still be alive. THAT is why I'm thankful I failed at cutting my own story short. THAT is why we should all strive to live our stories until their absolute possible end; where they do so, without our own intervention. Do it for your readers. Do it for your watchers. Most importantly, do it for yourself.