And perhaps people not only forget that all suffering is temporary, but they also realize that all happiness is ephemeral as well. Two-fer downer right there.
Such might lead one to say that all is vanity, after the fashion of the Teacher, hm?
They may be ephemeral, yet that is only a dismay if one takes one's mood to be the purpose for living. That is, if you expect it and think that life must be joyful, you are doomed to ever be disappointed, and all that you experience fall short. Yet if you resolve to only take what is given, bad and good alike, do what you can to your best, fight a good fight in life, why, is that not itself something?
There is always beauty. Because even if happiness is ephemeral, joy is not. One is a dependance on emotion and mood, and the other is a resolution and peace and acceptance of the way things are. Not that one shouldn't strive to be better, but there are things that are beyond our control, and if we live our lives requiring those things to be fulfilled for our happiness, we shall never be happy.
How can we possibly expect to be happy when we set our happiness' store on the whim of capricous chance?
Do not be overly happy, nor be depressed. One is too much feeling, and the other is no feeling at all, and one extreme will inevitably lead to another. Be happy with what life grants you at this moment, even if it's not something that is overtly good. Do not shirk to frown, do not put on a pretense. Weep when the time is right, and laugh when the chance arises, but keep you mood level. And contemplate circumstance and feeling always. Then nothing is ephemeral.
Vita satis est.