Human beings are scary.
We breathe a corrosive gas, drink one of the most potent solvents. Our preferred method of hunting was persistence hunting, where we chased animals until their body simply gave up and died. We can eat just about anything we find, which means that we don't need to stop for food when chasing our prey. If we can't find food, that's fine. Our body will simply begin to eat itself so that we don't have to stop chasing our prey. We walk upright, we sweat, we don't have much body hair, which allows us to radiate away our body heat. This means that excessive time or extreme environment wont stop our hunts. If the animal fights back against us, we can take massive damage to our extremities and lose half our blood and still live. Our entire existence is owed to persistence, endurance, and determination. When we put ourselves to a task, it gets done, period. And this instinct is still affecting us today.

332BC: Alexander the Great hits a stalemate with the fortified island city of Tyre. Instead of going back defeated, he builds a kilometer long bridge in order to raze the city.

49BC: Cesar, after defeating the Gauls and invading Britain, turns a political fight into a civil war by invading Italy with only a single legion. He eventually becomes dictator starting a world superpower whose engineering feats are only recently being broken.

1804AD: A charismatic French general declares himself Emperor and sets off to conquer much of mainland Europe. He is captured, exiled, and then escapes. The soldiers sent to recapture him instead lay down their arms and join him.

1961AD: One man decides that we will go to the moon, despite much of the technology to do so not even existing yet. Just eight years later, two humans stand on the surface of the moon and look back upon the Earth. 200 years ago, we didn't have railroads. 100 years ago, we didn't have airplanes. 50 years ago, we didn't have spaceflight. 25 years ago we didn't have the Internet.

We've already inherited the Earth and soon we WILL inherit the stars and anyone or anything that stands in our way will be eliminated one way or another."