The best teacher I ever had was a sociology professor at Haverford College named Mark Gould. I’ll never forget the first day of the first class I took with him. He basically spent 90 minutes scaring the shit out of the two-dozen 18- and 19-year-old students in the room. He handed out a syllabus featuring an impossible number of books we were supposed to read over the course of the semester. And none of them was Black Beauty. Rather, the included Georg Hegel’s The Phenomenology of Spirit, Karl Marx’sCapital (Volume 1), Emile Durkheim’s Suicide, and the like. Gould told us that we did not know how to think and his job was to empty out all the crap inside our skulls and essentially restart our education from Square One. Eight students returned for the second session two days later.

Mission accomplished, as far as Gould was concerned. Knowing that not every Haverford freshman was teachable—or at least not teachable by him—he made a systematic effort to get rid of the young minds he’d only be wasting his time with before he actually wasted any time on them.

I do something similar as an endurance coach. In my experience, not every athlete is coachable—or coachable by me, anyway—so I engage in some pretty stiff upfront vetting to weed out potential clients I suspect I won’t be able to help.

I’ll give you an example. Not long ago I was contacted by a triathlete who was interested in hiring me to create a custom training plan for an upcoming Ironman. He told me that running was his weakness and he wanted a plan with high running volume, which he viewed as necessary to achieving his goal of breaking 10 hours.

Anytime a potential client tells me how to train him or her, I see a red flag. It’s a sign that the athlete thinks he has it pretty much figured out and will resist making changes I view as necessary to produce optimal results. In this case, I explained to my potential client that loading up on running miles is in fact not the most effective way to maximize Ironman run performance, and that getting really strong on the bike and doing a lot of running off the bike have a bigger impact. My intent was not to get rid of the guy but to let him know that if he wanted me to create a training plan for him, he would need to accept the program I deemed best given his strengths, weaknesses, and goals.

To my mild surprise, the athlete asked me to go ahead and send him the questionnaire that I use to gather the information I need to build a fully individualized program. When I got it back from him, I discovered additional problems. He specified that he wanted a 12-week plan that would begin immediately after he completed an Ironman 70.3 and would end on the date of his Ironman. Additionally, he expressed a desire to complete a number of “B” races (one or two sprints and an Olympic-distance event) within this span.

Pure insanity. This athlete was giving himself 11 weekends to build the endurance he would need to complete an Ironman in less than 10 hours. The first and last of these weekends could be tossed out as opportunities because he’d be recovering from his 70.3 in the first and tapering in the last. And if he did all three proposed “B” races, three more weekends would have to be eliminated, leaving him with six. The icing on the cake was that this athlete only rode his bike twice a week. He seriously thought that his best chance of crushing the marathon in his upcoming Ironman was to run 50 miles per week and cycle twice!

Now, there’s absolutely nothing wrong with not knowing what you’re doing as an athlete. That’s where coaches come in. But there is something wrong with not knowing what you’re doing and thinking you do. In my next email to this athlete I told him that I thought it was a bad idea for him to do any “B” races between his 70.3 and his Ironman. He never replied, convinced now that he knew better than me. But here’s what I know: that poor fellow is going to have a rough Ironman.

People hire coaches because they need help and they know it. They have goals that they believe they can achieve but are unable to achieve on their own. They know they need to do some things differently. And yet many athletes who reach out for help from coaches prove resistant to making changes. They are either set in their ways (“I refuse to run on pavement!”) or they don’t entirely trust their coach (“I don’t see how doing hard intervals is going to help me run a faster ultramarathon!”) or both. Such athletes are uncoachable—not completely uncoachable, usually, but uncoachable to a degree.

Hiring a coach is an act of humility. But to get the full benefit of working with a coach, you must commit an act of faith by allowing him or her to change things, even if some of the changes seem wrong to you. To do otherwise is to try to have it both ways, refusing the help you’ve admitted you need.

By no means am I suggesting that the coach-athlete relationship should be completely one-sided, with the coach allowing no input from the athlete and the athlete being completely submissive. Any good coach welcomes a degree of skepticism and pushback from athletes and is willing to accommodate their training preferences insofar as they don’t violate the coach’s principles. And yes, there are bad coaches out there who steer athletes in the wrong direction, but it’s the athlete’s responsibility to choose a good coach. Once you’ve made your choice, you need to let your coach do his job. Give him a chance, and if he does steer you in the wrong direction, then move on.

At a more general level, this advice applies also to self-coached runners. Don’t expect to get different results from doing the same training. Be open to the possibility that the reason you aren’t fully satisfied with how you’re performing in races is that one or more of you current training habits are badhabits. Accept that some of your current beliefs or assumptions about how to improve as an athlete are probably wrong.

Whether you have a coach or not, one of the keys to overcoming the obstacles that stand in the way of your improvement as an athlete is a willingness to learn and change. It’s important that you be prepared to let go of practices and ideas that are exposed as potential obstacles by outside experts who have a track record of helping athletes improve.

As an athlete myself, I understand how tempting it is sometimes to defy a coach’s guidance—and how risky. When I trained with Northern Arizona Elite last year, one thing I found strange about how Coach Ben Rosario managed the stable of professional runners training under him was that he really babied them after races, even short ones. When I travelled from Flagstaff to Portland to run a 5K midway through my marathon training cycle, I ignored Ben’s instruction to take the following day off and instead did an easy 12-miler. After all, he wasn’t there to stop me and I felt I knew better. Upon returning to Flagstaff, I suffered a serious injury during my first workout back with the team. Lesson learned.