Stress

If the slow pace of golf and the soothing whispers of sports announcers stress you out, then finding a job as a caddie is the least of your problems. Obviously, there are going to be moments when your next paycheck hangs in the balance. 

After all, tips aren't guaranteed and Tiger might actually miss that tournament-winning putt. But for the most part, working as a caddie is one long, glorified walk that shouldn't stress you out all that much.

 
"So, if I miss this putt...it's not exactly your fault, but you're fired." (Source)

Of course, if a golfer is trying to win a major tournament and turns to his caddie for advice on the decisive eighteenth hole...that caddie is going to feel some pressure too. But being on the cusp of winning a major tournament is an ideal position, even for the caddie, so it'd probably be more exciting than anything else. Let us know how it feels when you get to that point, alright?