For starters, Arapahoe Basin is not the best place to learn to do any snow sport that requires control. The green runs at Arapahoe are close to easy blues, mostly due to the steeper grade of the slopes.
Second, while snowboarding is pretty easy to learn, its damn unforgiving when you mess up. Its easy to figure out how to ride an edge, but harder to learn to transition. When you fail to transition the edge of the board grabs the snow and stops. Your center of mass being two or three feet above the board doesn’t stop nearly as quickly.
So my first day of snowboarding involved many, many falls, especially when trying to turn around to cross the slope the other way. In all though, its awesome fun.