Have you ever broken a fingernail to the point where the nailbed is exposed? It's quite tender, and very painful when you bang it or rub it, isn't it?
Now imagine trying to press your nails into a baseball, pushing HARD onto the ends of your fingers, right onto that exposed nail bed. Sounds painful enough, but not too bad, you'd think.
NOW imagine the friction of that ball leaving your hand, rubbing against that exposed nail bed, and THEN think about doing it over and over and over again, for up to 120 pitches, and that doesn't include warm-ups. THAT gets painful!
If that doesn't convince you, have someone stick a needle under your fingernail, 120 times, over a 3 hour period. You'll understand what he's going through.
It's real easy to discount someone else's pain and discomfort when you haven't endured the same thing. And remember, too: if he's pitching in pain he's NOT going to be at his best, which affects not only him but the rest of the team, too.
All that being said, they STILL pay these guys WAY too much money. But as long as people are willing to shell out the bucks to go to games, and are going to let the sports and entertainment celebrities dictate what to wear, what to eat, what to drink and whatever else it is they do, the money will be there for them. At least now it's going to the players and not just to the owners.