I spend a fair amount of time on the letsrun message forums, and one point that comes up repeatedly is the concept of "two types of runners." You can read the entire thread here, but it reduces to the concept that different runners have different ratios of fast-twitch to slow-twitch muscles, and thus benefit from different training regimens.
The "two types" are defined by their physiology, but I think you can also classify runners by personality. Based on a ton of observation, my perception is that there are three types of competitive runners, from a mental standpoint. And just like the "fast-twitch v. slow twitch" classification, in which many runners fall in between the two extremes, I think of these classifications not as absolutes, but as different zones. There are many who fall into more than one of these buckets.
Type 1: These guys are characterized by their relaxed, fun-loving approach to training and racing. They sign up for racing because they enjoy the atmosphere, and pick races with fun shirts, nice goody bags, etc. They care about their training, but they also value other activities, sometimes (or frequently) skipping runs in favor of happy hours, work, bad weather avoidance, or just plain sleep. They are willing to shut down workouts early if the workout is not going well, though sometimes they are too prone to shut it down. Similarly, if these runners run into a difficult patch of training, their normal response is to take a break, and then return to running when they feel fresh.
These runners are rarely at the very front of the pack, but they are completely happy with that -- their priorities lie elsewhere, with friends and family and other commitments.
Type 2: Workouts are completed no matter what (and this type may show up at the track to do the workout on their own when it's cancelled, or when they've been told not to show). Rain, snow, bad knee, sore throat, major personal crisis, sleep-deprivation, they're there. This type tracks (and evaluates and analyzes and applies several other verbs to) nearly everything, including every single split of every run. Including the warm-up and cool-down jogs.
And they're always looking to do more, whether training is going well or badly. "Rest" is a relative concept; it may be given lipservice, but it's not followed in spirit. And it's easy to understand why -- to this type, "rest" is not very restful.
These runners are generally in the middle to the front of the pack, and they advance very quickly early in their training. But they hit an artificial ceiling well before they reach their true potential and the front of the pack.
Type 3: In actuality, this isn't a type of its own, but rather a distinct blend of types 1 and 2. These are the runners who are more "type 1" in most of their training. Easy runs are relaxed and informal -- they do what they need to do, but they feel free to skip a workout if they feel off or if there's just too much going on in their life. When it's hot and humid, they don't fret about slowing down or cutting the run short.
However, these are also the runners who are able to magically swap to "type 2" at the right moment -- during a key workout or a race. When it really matters, they turn it on and give their all. They are flexible, going back and forth between the two mindsets as appropriate.
My observation is that the "front of the packers" are almost universally type 3s. And it's been eye-opening to recognize this.
I'm a solid type 2, and I'm reasonably sure I'm not unique here. When my training's going poorly, my overarching instinct is to train harder, to fix things. To the point where, after a bad workout or race, it's very hard to resist the urge to go out the next day (or even that afternoon) and do a hard workout to compensate. I do resist, but it's a struggle.
And of course, when my training's going well, I want to train harder -- to strike while the iron's hot. I get greedy.
I actually believe that nearly all competitive runners are type 2s, to some extent. Simply because it's a certain type of personality that is drawn to running to begin with. And also because the culture of training logs and plans, discussion boards, Garmins, etc, encourages that type 2 personality.
I've been lucky enough in the past few months to be able to run with some very successful runners. And I've noticed that they're consistently type 3s. That seems to be the mentality of the runner that makes it to the very top. They maintain a healthy perspective that carries over to easy runs, warm-ups, cool-downs, and rest days (I've noted particularly that people much faster than I run their warm-ups and recovery jogs much slower than I, and are much more comfortable in skipping days).
And yet, these guys are able to flip the magic switch at the right moment, and shift to type 2. More importantly, they are able to distinguish when it's appropriate to be a type 2 (i.e. finish the workout no matter what), and when it's appropriate to take a break or cut back.
The conclusion's pretty obvious -- those of us who are type 2s are held back by our tendencies, and will never reach our potential until we learn to back off a bit, and not sweat (literally) the small stuff. So why don't we?
Easy. It's insecurity. A lack of confidence in one's running leads to a constant search for reaffirmation, be it in the splits at the end of an easy run, or the miles in one's training log. A bad workout is an emotional blow; thus the urge to prove to oneself as quickly as possible (by running hard the next day) that it was a fluke.
Moreover, many of us type 2s fear that we don't have the mental strength to be tough unless we practice it constantly -- if we relax and adopt the type 1 mentality, we won't be able to turn it on when it counts. Or we may even see ourselves as type 1s, who have only advanced as far as we have due to constantly fighting our natural tendencies.
Becoming a type 3 runner is all about self-confidence at the end, and that's what makes it so hard. You need to believe in both your fitness and your mental toughness, without proving it to yourself repeatedly in workouts. You need to be secure.
I don't know quite how you get there. But it seems that if you have the discipline to push everyday, you should have the discipline not to push. One hopes. The alternative is that you never reach your potential, and that's not terribly appealing.