I'll just come right out and say it. I'm a pretty darn good mountain biker. I may not be the fastest, but I can stay toward the front with most of the groups I ride with, and I have pretty good technical skills. At the Spokane Mountaineers mountain bike school, I usually teach the more advanced group. Yep, not a bad rider.
I'm a pretty decent skier, too. I don't have the prettiest form, but I can ski all of the local terrain, and I do pretty good, in even the worst conditions. I'm still working to master breakable crust, and I realize that thinking you can ski a double black diamond in Alaska, because you can in Idaho, will get you killed. But still, all in all, I'm a good skier.
I suck as a swimmer. I started swimming last summer, because my back hurt if I ran too much, and my prostate didn't want to ride too much. In other words, I started swimming because I'm getting old. It's a nice low impact sport (if you consider drowning low impact). I started out in the river, by myself. The first time out, I swam about 10 minutes, and thought I was going to die.
I kept going back, even bought a wet suit, and got to the point that I could swim for 20 to 30 minutes at a time. Still by myself, though. Then this winter, I joined the gym, and started swimming in a pool. With other people. And I suck. People I have never talked to come up and give me tips. I'm sure they stand there, trying to decide if they should say something, and then they just can't stand it anymore. With the words, you suck, screaming in their heads, they tell me to keep my head down, try to keep my butt up, rotate my torso, and stop whatever the hell it is I'm doing with my legs. I nod, thank them, and then flounder down my lane, head up, butt sinking, torso flat, and legs doing whatever the hell it is that my legs do.
I know that in 10 or 20 years, I probably won't be mountain biking much, and my back will have deteriorated so much that I won't be able to run at all. All that I will have left is swimming. Great.