Things informed runners would admit to if injected with a strong barbiturate
A lot of people do good things for good reasons, such as working multiple jobs to support their families. People also do not-so-good things for good or at least defensible reasons, such as stealing food to stay alive or exacting various forms of revenge on physically abusive spouses.
Moving down the urgency scale, people often maintain vaguely defensible or sketchy practices when it comes to their serious hobbies -- not because they really believe that these practices are beneficial (or at least harmless) but because they are enslaved by them. As cognitive-dissonance theory predicts, such people search for rationales to logically justify habits their psychological make-up compels them to do anyway. A person who embarks on a spending spree in the midst of a manic episode might claim that the reason he just put $2,000 worth of CDs on a credit card is that he really likes Justin Bieber, and he might even convince himself that this is true.
Runners, being more compulsive than most, are a hotbed of such rationalizations. When we knowingly do things likely to impede our competitive development, handy rationalizations are always within easy reach: I don't need to taper for this race, it's just a 5K. I don't need to do over 40 miles a week for a half-marathon if I get in plenty of long tempos. I can be kinda sorta bulimic and run well if I manage it right. Anything slower than x minutes a mile is just junk, so why even bother?
Below is a list of rarely expressed truths or de facto truths in the running world. Most people who have been around the sport for a while would not disagree with any of these statements, but in most cases would not want to be the person volunteering them, as a few are more controversial than others. (Understand that this is not a list of common running myths, which are different in that myths, in this context, are things people mistakenly believe to be true.)
"Cool-down" is a misnomer, and cool-down runs are little more than a way to pad mileage totals and gab. They certainly don't make anyone feel less tired or speed up recovery.
Virtually no world track and field records are "clean," and at the elite level, drug testing is a joke.
Watching marathons on TV or the Web is boring. While unprepared running commentators don't help the quality of broadcasts and webcasts, road races are so intrinsically uninteresting on a moment-to-moment basis that even Robin Williams, unchained and on coke, couldn't have made them interesting.
The idea of "balance" in the athletic world is absurd. No one who wants to be great at anything that requires work enjoys anything resembling "balance" as the self-help yutzes define it. Some people thrive on being one-dimensional if they are sufficiently good at that single diminsion.
You can subsist on an abhorrent diet and still run well. You might pay a price later, but general health and top running performance are weakly correlated at best. Perhaps a better way to express this is that tripling your food budget in the belief that it'll make you a faster runner is a waste of money.
Along similar lines, you can smoke weed, snort coke, and drink to excess and be a national-class runner if you pick your spots, as well as your parents, correctly.
Intelligence is overvalued in running, just as it is in most sports. If you cannot think of a world-class runner who strikes you as an idiot within a few seconds, or one who seems to have it together but frequently blows up in races for clearly mental reasons, you may be new to the sport.
East Africans are not somehow tougher than elite runners from elsewhere. When things aren't going well, they will unpretentiously jog it in or call it a day, and some will fake injuries in the process. (If any nation deserves a "toughest runners in the world" distinction, it's Japan.)
Most runners harbor secret thoughts of setting personal records for at least five years beyond the point at which this is remotely realistic. Sometimes longer. Lots longer.
This one is gratuitous, but just about everyone who has been running for more than, say, 10 years could fill a one-hour podcast with florid descriptions of the times he or she perpetrated explosive sharts during a run an then had to get home somehow without being declared a Superfund site. (I was once about two feet away an unfortunate and especially violent episode of this type, this and her eyes bugged out so hilariously, like Eddie Murphy in his "Mr. Robinson's Neighborhood" skits on SNL in the '80s, that I almost crapped my own pants.
(3/27/18 10:46 a.m. edit: I should point out that I don't think all of these things are universally true; they can't be, since some of them deal with subjective concepts. I do believe that far more people at least think them than would ever express them, and for defensible reasons.)