The Earth still contains many mysteries (hello, ocean), but they pale in comparison to everything that goes on in outer space. Miles have nothing on the incomprehensible stretch of light years, and there are way more galaxies out there than there are species in the animal kingdom. It's mind-boggling to think of how many undiscovered planets are out there, let alone the fact that something like a black hole exists.
All of it is liable to make somebody feel very, very small. No matter where we go and what we do, we're completely insignificant in the grand scheme of things. Let's look on the bright side, though — there are all these cool things out in the universe just waiting to be explored. Even better, they are ripe for making a load of dumb memes about. The enigma of the great beyond is pretty funny if you try hard enough to make it that way.