Racing in general is a very humbling experience. I never bothered to try the GNCC at Snowshoe because I knew from spectating that it was brutal. After doing a few desert enduros out here I know just how brutal it is. I mountain bike regularly, don't smoke, etc. But half a lap on an enduro track (~10-12 miles) or a few laps on an MX track is enough to have me at O2 redline.
The few races I've done so far, I know when the A guys are lapping me, because I'll hear an engine pinned for about 2.5 seconds before a bike whooshes by me in a cloud of dust.
Stubborn and Stupid
"It's supposed to be a challenge, that's why they call it a shortcut. If it was easy it would just be the way." ~ Rubin, Road Trip