You're running a relaxed 4 mile run feeling like the Jamaican Olympic Track Team and as you approach your mile 3 point your Strava/Nike+/Map Your Run App tells you you're at Mile 3 and blah, blah, blah. As you turn the corner you run into your ex with her/his gorgeous and impeccably dressed new love. After a perfunctory wave and as you strain to change your running form into what can be called Usain Bolt Lite you collapse into a heap of sweat and heavy breathing and formless mass onto the street (or at least you think you do.) You click on your "Power" song which now literally makes you collapse onto the street ground and moan and drool diluted Gatorade not noticing your Ex and new mate have come back and are asking you if they should call an ambulance.
You've discovered that thinking is a behavior and while this is an extreme example that absence of negativity is not positive thinking. Several running studies have demonstrated, especially in endurance racing, that psychology has as much to do with physical conditioning on getting through the later miles of an endurance effort. A negative thought can indeed collapse physical effort and the challenge is that like your physical conditioning every aspect of your life plays a role. Repeated mental exercise, repeating mantras, and visualization are just the beginning of engaging positive mental image and durability but all of our lives also have consistent negative reinforcement as well: how could we not? Life does suck sometimes and we manage by defusing through fear, sadness, anger. You can chant "Serenity Now" as much as you like but insanity does come. Later.
While our example used a negativity that literally stepped out of nowhere, and physical in nature, this is exactly how negative debilitating thought can hamper performance. All of us have experienced this. Wellness tools can help you train your mind to be more resilient.
Have a friend or coach (coach ain't your friend) do an honest assessment of your outlook towards training and the race and in your abilities overall. We've had athletes who worked harder than most and for many they did so because they did not believe they were capable. They'd boast of attacking the race until they were asked what do they think their time would be and things began to unravel going from, "I'd like to just finish" and reaching, "I'm not even sure my last training session will get me to the race." If you don't understand what your true posture/attitude is then you're burying the negativity which only requires a bad T1 or T2 to come out. Assess whether your outlook matches what is being perceived by others and if the delta is great then bring the concerns to the light and plan how to engage the concern.
You have a physical training plan. You need an emotional and mental one as well. Your goals not only include time, power, and skill but a process based approach on engaging negativity. In triathlon swim induces panic, cycling mental fatigue, and running surrender. You have in fact developed process based approaches to each: in the swim you may focus buoy to buoy, in cycling recovery through positioning, and the run self induced speed variability. Learn from your approach and if the thought that you're going to be audited by the IRS pops up in mind process that 1) they ain't going to do during the race and 2) jail will provide you lots of time to strengthen your core. Create a process plan for each session and throw your self a doozy in the middle and practice climbing out of it. Cause negativity is a self fulfilling piece of sh!t and no matter what your conditioning can spiral out of control.
Log and measure your sucks. Some workouts absolutely suck even though you PRed. Look at a week and look at how many sucks there were and you'll find many were due to emotional/mental collapse and not physical. But you will also notice, guaranteed, that you had way more good workouts than not. Analyze the sucks and talk them out. Find that friend who'll listen to your dumbest crap or a coach and talk it out - once out you can process it and develop a strategy.
Perception of fatigue is fatigue. Your mind can make you collapse even when you're firing on all cylinders: well proven and known. But how to stop it? Reframe it and refocus. How many times have you done a 10K when mile two sucked and mile 4 through 6 were the best run ever? Most likely you focused on how much the run sucked and your mind wandered onto something totally unrelated and allowed for you to recover emotionally. Do that. Practice it. When the thought comes up reframe it and put it in perspective with what you've already accomplished or are going to. Another strategy is to take your mind to the physical performance: listen to the sound of your steps, watch your shadow run, take a sip of water and focus on that. You'll notice fatigue slip away.
One of the questions I always ask an athlete is why are you doing this? Therein lies both the power to stave off negativity (notice not eliminate) and use positive thought exercise to strengthen endurance. Training 140.6 athletes I ask them to truly assess the why. The race is so freakin long that every thought comes up and that by mile 120 of the thing the medical tent starts to look really good. What thoughts will keep you doing the left foot-right foot thing?
Know your weakness, bring it with you to training, track it, and embrace it. Then process it.