"Awright soldiers, it's time for you to learn about the enemy! Now, who can tell me just HOW an Enderman can teleport, WHY we get hurt when we teleport, and WHY they get hurt by water! And, if anyone is brave or arrogant enough to try, explain why the water dagger is just as effective on humans as well as Endermen! I warn you though, no one's been able to figure it out yet, AND if you get it WRONG, your whole floor gets no warm water for a week! Buuuut, if you get it riiigghht, your whole floor gets to shower first, guaranteeing warm water."
"Uh... I believe I can say how an Enderman can teleport, a-and why we get hurt sir," said a private who was seated in the back row. He then quoted his textbook word for word.
"An Enderman's molecules are spread apart much farther than our own. Any bits of matter that would strike it during teleportation go straight through it without causing any damage. Since teleporting is basically just moving at extreme speeds, even small particles of matter in the air can do serious harm in the event of a collision, so when we teleport, the matter hits and damages us."
"EX-cellent work, private! Now. Enlighten me on why they get hurt by water!"
The same private answered.
"It is because they have very unique blood. When their blood touches the water, it starts to become water. Since their molecular structure is so open, the water can get in and change them."
"ONCE again, you imPRESS me, private! Perhaps you also know how the water dagger works?" The trainer chuckled a bit, as the problem had been baffling the EDA scientists for years.
"Y-yes, sir, I can."
"REA-LLY... This better be good, or you'll be showerin' with the polar bears."
"I ran some tests, and found out that Endermen, but for a few minor evolutionary splits, are us! I tested by drawing some of my blood, capturing an Enderman, drawing some of his blood, and looking at them both under a microscope. Our closed molecular structure is the only reason why we aren't dying off whenever we go for a swim. But, since the water dagger pierces the skin, our defenses collapse. I brought the samples right here."
"And how, exactly, did you capture an Enderman? You know, the creature that can TELEPORT?! Son, your story is more full of holes than an Enderman is."
"Look at the blood."
"I don't have a microscope, so you just have to explain it to me!"
"It was simple. I made an artificial island, found an Enderman's egg in the wild, spawned one, and it couldn't go anywhere! Ocean for miles and miles around."
The general called for his assistant, and in hushed tones, told him to take the blood samples to the lab. The private was proven correct, so he went back to his floor a hero. (After all, warm showers are a big deal.)
Short note: Water daggers are standard issue EDA weaponry. They have been found to be just as effective on Steves as they are on Endermen however. This was found out when an EDA agent scratched himself on his dagger, and turned into a puddle.