That's usually what's going through my head during a workout. If we're doing something I really don't like, something like wall balls, I just try to think, "This will all be over in 5/10/15 minutes." That usually helps me get through it.
I watched The Amazing Race tonight (anyone want to sign up with me?), and they had to hang from this tall bridge or platform or something - something involving heights that scared the crap out of some of them. They didn't really have time to be scared since this was the final episode and there was a million dollars in sight, so they just did it. I think if I were in that situation and my challenge was really scary, like something in the water, I'd tell myself that it will all be over in an hour and I won't have to do it again.
Wall balls can be scary, too, especially when they hit you in the face.