When you were younger and (impossibly) more self-centered, you whined like the world owed it to you to listen. Eventually you learned that happiness should be shared, and negativity, in all its nasty forms, should be shelved. Nobody loves a loser.
So you keep the bitter, the sad, and the angry in specimen jars and examine each of them in your spare time, always having to be careful so as not to end up trapped in those jars yourself.
While you wish you could share them with someone, you almost never do, because you almost never can. Some miseries are simply inexplicable and are thus easier borne by one than by two.
So you keep on, and remind yourself to smile and laugh about the good things, of which there are quite a lot. In those small moments, the universe is wonderful and everything glows in the light of an idyllic summer sun.
And that light is enough to fuel you, for today at least--and for tomorrow, and the day after that--until one morning you wake up and there's more light than dark.
And that's how you know you've made it through, and can make it through again.