I don’t really like the “life is short” idea.
I mean, aside from the fact that around 80 years of life seems pretty damn long to me, that’s just so depressing? Your life is short, so hurry your shit up cos you’re gonna die pretty soon.
I get the idea - don’t waste time being sad because you could be happy instead. But personally I think life is long is way cheerier! Don’t be sad, you’ve got ages ahead of you! You have so much time to do so many things, and you’ll always be finding new things to do!
It’s okay to be sad and/or apathetic now and again, or of you’re after suffering a loss or something like that. But look at it this way, you have all this time ahead of you, so much time to do so many things and make your life so much better, are you just gonna spend all that time doing nothing? You’re gonna need to smile again sooner or later, so might as well get a head start on doing what you love.