1. Stop ignoring recovery. What you eat, how much you sleep, the beers, it all affects you. The intensity you go on easy workouts is also vital.
2. Stop doing everyone else's workouts, and start focusing on what workouts YOU need. Sometimes, (in fact many times), that means you need to train alone. Peer pressure is no way to train effectively. If you train with a lot of egos, let them go. Limit group workouts to those which are in line with your goals and specific needs. This especially includes recovery workouts. (See #1).
3. Stop sabotaging your training. When life gets stressful, skipping workouts because you're not in the mood only brings about more stress and frustration with training and lack of results. Training is your escape, keep it that way. Skipping that transition run because you think you're too tired, is a missed opportunity to build confidence with a great run, or to learn to better pace your bike.
4. Stop ignoring your weight. If you aren't thin, you aren't as fast as you can be. I'm not saying you should look anorexic, but to think those 10 lbs you could lose aren't affecting your performance, is ignoring the obvious. If you're 20+lbs over an ideal race weight, there is no training plan or lightweight bike that can overcome that handicap. The weight also means higher risk for injuries, which can sabotage your training. (See #3).
5. Stop ignoring your diet. (See #1 and #4).
6. Stop obsessing about volume. If it really mattered, the athlete who did the most volume would win every race. Ultraman competitors would be the best Ironman and sprint racers. It's about the quality of training you can do. You're not training for the Tour de France.
7. Stop ignoring the swim. The higher your goals, the more it matters.
8. Stop ignoring your warm-ups for your workouts and races. The older you are, and the higher your goals, the more it matters. It's like sabotage. (See #3)
9. Stop ignoring your cool-down sets, they are vital to proper recovery. (See #1) Poor recovery sabotages training and racing. (See #3).
10. Stop ignoring technology in your training. You use technology in every aspect of your life, from your iPhone/Android to your laptop and software at your job or at home. Why is it so hard to believe power and pace data can help your training and racing on a daily basis? (See #3).
11. Stop thinking you need a faster/newer/better bike. You need to get training right. (See #1 thru #10).
12. Stop paying a coach if you're not going to do the training as they write it. (See #3)
13. Stop being negative with yourself. There is nothing anyone or any coach can tell you that will supersede what you say to yourself. If you don't believe in yourself when you toe that start line, the result is pretty much already determined.
14. Stop focusing on the competition, and start focusing on yourself, and how to execute your training and racing better. (See #1 thru #13)
15. Stop doing the same thing over and over. The body responds best to variance in training. If you've been doing the same things over and over for years, and aren't happy with the results, or notice a plateau, it's time to address the real issue.
16. Stop thinking salt and electrolyte losses cause cramps, there's no scientific proof of this. The people who promote this are the ones trying to sell it to you. Get fitter, and you'll cramp less. Get training right, you'll get fitter. Stop shoving so much salt into your gut during races, and you'll likely get rid of all that GI distress you've been bothered by in races.
17. Stop thinking Ironman is the only important race in triathlon. It's far from it.