Intelligent people have a strong tendency to discount motivational platitudes and self-help books, because those sound (and often are) stupid.

Actually, the proportion of "actually stupid" to "just sounds stupid" is very, very low. The problem is that what you might call "action skills" and "satisfaction skills" do not operate using the same parts of the brain that "intelligent" (i.e. analytical) people are accustomed to using.

So, if you evaluate a statement using the machinery you're most accustomed to thinking with, the sayings sound stupid, even when they're not also phrased in new-agey or pseudoscientific ways.

I've found that most of my advances in personal development came after I realized that my intellectual bullshit-detectors were filtering out everything that was useful in the self-help field, simply because it wasn't true.

IOW, if you ignore the truthiness of a piece of advice, and simply attempt to adopt the state of mind and mental/physical behaviors given, you will very often find that the stupidest, most nonsensical theories are shielding you from some incredibly useful practical advice.