It's very hard to be an athlete and coach at the same time.
I've been very fortunate in my 25 years of training, in that I've always found people to look over my shoulder. I'm sure I know how to train myself better than anyone else knows how to train me, but I also accept that I don't know everything. I also recognize that no matter what, there's probably always a better way.
We'll never know for sure what the "best" way is, but something tells me that we miss more than we hit. Having someone look over your technique, training plan, diet, and other training aspects can save you time and mistakes down the road.
Let me say something here about programming. We all know there are different aspects to program development, ranging from (but not limited to) flexibility, strength, endurance, mobility, pre-habilitation, and all their subcomponents such as strength-speed, strength-endurance, dynamic flexibility and a host of others. The thing most people seem to miss is that you can't have it all.
Think of it as a stereo equalizer, with each aspect having its own control. It you were to slide all the controls to the right, you would hear distortion (overtraining, imbalances, injury, etc.). If you were to slide them all to the left, you wouldn't hear anything (no training: no results).
The key is to find the right settings that produce the perfect sound for the goals you're training for. This is where a coach or someone with experience can help out because what you're used to hearing may not be the best sound because you've become accustomed to it (your cheap Walkman sounds great until you walk into a BOSE store).
The other thing to remember is that there are lots of different settings, and what sounds good to one person might not sound the best to you. If you're getting the results you want, then you're good to go.
Finally, if you do ask or seek help, then shut the hell up and listen. If you asked the right person, then they have something to offer you. Even when you don't ask, keep your ears open. Believe it or not, there are people who are better than you, and who know more. They just might say something that can help you. You may have been missing something that they were able to spot.
People always ask me, "Knowing what you know now, would you have changed anything about your training or diet from years ago?" My answer is always the same: no. You can't turn back the clock and change the past. You can only do what you can do today. I see no reason to answer what I can't do anything about. Do I offer people different advice now based on what I feel were my mistakes of the past? Yes, of course. I've made some huge mistakes, but they were necessary, because without them I wouldn't have learned anything.
The best way I've found to use coaches is to make your training result a team effort. So you're not just training for yourself, but for everyone who's involved in the process. When all is said and done, they'll get (and deserve) the credit, but you're the one who'll get the result.
I have and will always consider this a fair trade, and because of this I've been able to enlist the help of many of the best coaches in the world. You may recognize some of the names: Alwyn Cosgrove, Justin Harris, Dr. John Berardi, Dr. Eric Serrano, Jim Wendler, Louie Simmons, Todd Brock, Chuck Vogelpohl, Joe Defranco, Dr. Ryan Smith, and many others. Without their help over the years, I wouldn't have been able to achieve all the goals I had set for myself.