Look, teeth. Now give us your money.
3. The more you brush your teeth, the merrier.
This common misconception lies in the concept of "if you clean something twice, it'll be cleaner than if you cleaned it once." While true to a limited aspect, brushing your teeth rigorously eight times a day or every time until you can taste your natural saliva again is not generally a good idea. The thing about brushing your teeth is that it's not a magical wand that you can simply wave at your teeth and only expect positive things. Think of this analogy, if you keep mopping your brand new wood floor, your floor is eventually going to collapse.
And everyone you've ever known will die. This is shaping up to be a bad analogy.
The thing is, excessive brushing can lead to other, more serious oral complications. For example, by brushing your teeth religiously, you risk irritating your gums to the point of exposing the roots of your teeth. Along with that, by brushing like a crazed manic, you also risk destroying your teeth enamel, and therefore your teeth itself. Everyone knows that your teeth are among the strongest bones in your body, most if not all of that strength comes from the enamel. By continuing a practice of excessively hard brushing, you could scrape away at the enamel like a waxed floor in a congressman's living room.