Stress
Golf is an odd sport; it punishes more than it rewards. That is, bad shots are punished much more than good shots are rewarded. Golf is all about hitting the ball at just the right angle, with just the right power, to get it in just the right spot. There's a core stress there that just never goes away. The possibility you'll get something wrong is a shadow that forever hangs over every shot.
The stress is quiet and subtle really, like a shark sneaking up on you in an underwater library. It's the fear of that dreaded putt that lips-out from four feet away. Or the shanked drive. Or the crisis of confidence known as "the yips." To take on this sport, you have to be something of a masochist and something of a warrior at the same time. If you can take the pressure, you're already way ahead of the pack.
And yes, you'll almost certainly miss big shots at important moments. Sorry, it just happens sometimes. When it does, try not to go Happy Gilmore in front of the cameras. That's not the kind of highlight you want making the nightly news.