Power
Off the field, the umpire barely registers in the consciousness of the baseball-loving public. You may be living out of a suitcase, traveling from Comfort Inn to Comfort Inn throughout your particular region just like the ballplayers, but no one is lining up to ask your opinion on last night's game.
Meanwhile, your bills and mortgage payments are piling up, your kids may be making all sorts of bad life decisions, and you probably have league office bureaucrats breathing down your neck. During the post season, you're stuck waiting for the people in charge to decide whether to use your service next season. You don't even get to hang out at the ballpark off-hours.
But on the field, it's you who is the neck-breather. You are The Decider of Fates, The Caller of Shots—the Baseballius Maximus, if you will. And you are expected to use that power on every single play.
Depending on your position in the crew, you may be calling every ball and strike as you see them, if someone is out or safe, even whether or not a ball that hits a player's head and bounces into the stands is a home run (it is).
Players and coaches can yell at you, spit near you, and even get dirt on your shoes if they're feeling particularly angry or brave, but with one small flick of your arm, you can get them out of your face and send them out of the game to an early shower.
The bottom line is, if you want someone out, they're out. And who's going to argue with you? All that rulebook memorization you went through really comes in handy here.