Time.

[AoU]

Time, the real final frontier.
Once we as a species have mastered this deplorable human concept and can finally grasp that time is our enslaver. We have let ourselves be pimped out by time for too long, fellow humans. We need to band together and conquer time, in the final effort to save humanity. Soon the days foretold will come to pass, and then you will be left behind. We will all be left behind.
There is no choice in the matter, time is the final enemy that humankind must defeat before our ascent into the ranks of the galaxy's most powerful species. Earth will be the talk of the town among the folks of every other sentient species that has surpassed this barrier before us, each of them congratulating us on our newest scientific achievement. We can not survive as we are, the planet is overpopulated, and it's only going to get worse as the End of Days comes.
To save yourselves from Ragnarok, the only route is through time!
Cut a swath through this primitive concept, and by doing so carve our place in the galaxy!

[Briar]

We can never grasp the perseption of the universe because we are limited by time.

[Sabriel]

Perception? What's that?

[Ungatt Trunn II]

PERCEPTION IS AN FUNNY WORD

[AoU]

Nipple.