Last month I went to Norway. Everything was white and full of snow, it was beautiful.
I stayed in a hotel (which name I don´t remember) and tried to do some snowboarding. I had done it only once before, but quite a long time had gone by.
So there I went, with that naive thought that it would be easy only because I skate, skim and surf. I put on my gear and the cable car took me up. I mean, it wasn't even one of those hard tracks, it actually looked like something that would be easy to accomplish.
Once I got up there, I made sure the snowboard wouldn't fall out during the descent, (turns out I didn't even needed to do that, you'll see why) I put on my goggles and I stood there, with a "victorious" look on my face.
Now let me explain the following part. The track had this "flat" part where I was and then it had the downhill. Well I was in the flat part and I made my way to the start of the downhill with little jumps. When I got to the edge, I stood in the right position (I'm goofy) and I threw myself.
Let's put it this way: I didn't last long. As I started going, I tried to take a little turn to the right. Result: disaster! I rolled, slid and rolled again during the entire descent.
When I finally stopped, not only was EVERYONE staring at me, but I had also dropped my goggles somewhere on the way and I was covered in snow, both my body and in my mouth.
I slowly (to make sure I wouldn't fall again) removed the snowboard, spit the snow out of my mouth and tried to clean myself a little. I was so tremendously bad that even a 7 year old girl made fun of me.
So I a walked back to the hotel thinking that there was no way someone could have ever been more embarrassed than me.
I obviously kept trying and training, and eventually I was able to go to one of the hardest tracks. Well not really, but I got a teacher and I totally mastered the first one (even though I tried not to pass near that spot for a while, so that no one would recognise me).
Conclusion: just because pros make it look it easy, doesn't mean it is. Not at all. It's very hard and don't think that just because you surf or skate, it'll be easy. You may have a small advantage over those that have never stood on a board before but it still takes A LOT of practise and training. Like any sport or anything in life.