Here's a picture:
Nature is not human-hearted. The sun is a huge ball of hydrogen and helium, fusing into lithium and carbon and eventually iron, on its very gradual way towards becoming too hot and dense to contain itself. Around five billion years from now, it'll consume itself and take everything in the inner solar system with it. The elements flung off from the death throes of the daystar will in turn birth new solar systems, and so it goes.
And the heart is not much more than an engine forged from the remnants of past dead stars; it too is subject to the laws of entropy, and will give out at some not-quite-certain point in the future. And the fortunes of most people are governed by similar laws: rise and fall, peak and trough, but the general trend is towards decline and extinguishment.
Point is: don't let some threadbare cliché fool you into thinking that hard times always come to happy endings at some predictable point in the narrative. This is real life, and not the stories we tell ourselves about real life. Anyone who's stayed up all night waiting for the sunrise knows what I mean: by the time the sun's rays begin to illuminate the upper atmosphere, you regret staying up all night and want nothing more than to go back to bed.
Practical lessons to take from this: (1) try to see a sunrise on a regular basis, because they're glorious and worth waking up early for, (2) get some sleep while you're at it, and (3) try not to sink into a pit of bibbering despair when things go south. Because sure, the universe is trending towards entropy, but it's no excuse to not try and make something of it in your brief tenure as participant and witness to the universe's unfolding.
