As a tall, skinny dude, I always like to joke that my weakness is my strength. After typing that I realized that it could mean that I'm really strong and that is a weakness, or how strong I am (not) is my weakness. While I consider myself athletic, it's the latter...
As with anything you do, strengths and weaknesses are an important factor in Ironman training. You have to plan your training accordingly, and both sides can affect your training a great deal.
I think everyone knows that the best things to work on are your weaknesses. As a veteran marathoner I figure that my strength will be the run. Therefore, what I need to work on the most is the swimming and biking. While I knew how to basically not drown, I started learning how to swim for real last Spring. Seems like that is going pretty well, and I think the lung capacity and cardiovascular endurance I've built has certainly come in handy. That didn't come right away though. Breathing while running is COMPLETELY different from breathing while swimming! As for the biking, I have strong legs from running, so the back/shoulders and butt are likely going to be the problem spots :)
One of my biggest weaknesses is my lack of will-power to STOP doing things. Like when I don't take enough time off for an injury. Or, the latest problem: I couldn't say no to playing basketball this year (where I get at least one injury a season) even though I'm training for an Ironman - which is the most important goal right now. So after a good first month of training I proceeded to "tweak" my knee at last week's game, ever so slightly, when I was coming down from a jump shot. Hopefully a tweak is all it is, but I've tried swimming and biking and now I'm resorting to time off. The worrier in me is concerned about the medial meniscus. Keep your fingers crossed for me that I heal up quickly...
[Just signed up for kickball this spring - that seemed pretty harmless...]
Lastly, I'd say I have a lot of heart, will-power, and grit. Those things have gotten me through a few races in the past - including most marathons, probably. There's a part of that which scares me. I know that I can push myself past my limits. That's great for an Ironman, and perhaps even necessary, but then where's the line? I don't plan on quitting if I feel like crap, but I sure as hell am not doing this all to not finish the race.
