Feel free to add to this list or argue (I know you all will anyway).
1.) I keep reading in articles that muscles either shrink, grow or stay the same; you can't "shape" them or "tone" them. Bullshit. Once, I religiously and progressively back squatted for about six months. My legs blew up, but they looked like shit: mostly the inner thigh muscle got bigger and nothing whatsoever happened for the vastus medialis. I quit back squatting. Later, I took a capoeira class (a Brazilian martial art where you basically lunge and kick for an hour straight) three times a week. At the end of three months, my thighs were more cut (not bigger: more cut) than they've ever been, and the vastus medialis more developed. The truth: different exercises develop muscles differently; it's not all just "bigger" or "smaller." Nowadays I do front squats: after two years of progressively heavier weights, my legs still aren't as cut as they were when I was doing capoeira, but they look a hell of a lot better than they did when I was back squatting. (As a sidenote, I think back squats work well for ectomorphs and mesomorphs: I've trained friends who were both, and their musculature developed very differently from mine, though I had them doing back squats).
2.) Getting a six pack involves a complicated program, is impossible to maintain year round, and requires crazy amounts--or intensities-- of cardio. Bullshit. I am extremely endomorphic and I keep my six pack year round (though, admittedly, I keep things tighter in summer). The secret? Three tough fullbody workouts a week lasting one hour, no cardio whatsoever. It's the food, dudes. If you drink juice and/or soda, no abs. If you love bread, pastries and dessert, no abs. If you don't consider it a real meal unless there's some starch on the plate, you got it, no abs. You must learn how to eat, if you want a six pack. Conquering your lust for sugar/potatoes/rice/bread and learning to love fish/green vegetables/cooking-not-microwaving is the deciding factor for whether you'll ever have a six pack.
3.) Related to the two points above: If you think you can follow the training or nutritional advice of just any author, you better think again. Back squat! Bench press! Barbell rows! Hold on partner: I pointed out how back squatting doesn't create aesthetic muscle for endomorphs. Extremely long arms? Think twice (think three times) about bench pressing. Got a bad lordotic curve? Think again about barbell rows. You've got to bring a lot awareness of who you are--your weaknesses and body type--before you accept someone's advice or think that it applies to you. I don't have to eat a lot to stay 200 very solid lbs at 6'--it doesn't take 6 meals a day or tons of calories; my metabolism is VERY slow. When an extremely ectomorphic author like Berardi gives nutritional advice, I have to take it with a grain of salt. You should too.
I could go on, but I'd like to hear some of what you all have learned that contradicts the messages we receive.