I've been on Mount Stupid a lot, maybe enough to be past Mount Stupid's Mount Stupid. I've had a lot of interests that I've developed over the (relatively short) 22 years and I've been caught standing atop Mount Stupid (by others and by myself) enough that I often feel it in the pit of my stomach - a sort of combination of embarrassment and guilt - when I start shouting from there. Especially if no one corrects me and I realize my mistake. The worst is the feeling I get when I've established some authority in someone's eyes and give them wrong information.
The best cure I've found for getting stuck atop Mount Stupid is to start learning a subject that's been the long interest of an honest friend (someone who's default mode of communication - at least among good friends - is significantly closer to Crocker's rules than to ordinary conversation). That seems to have really been the most helpful thing for me. If you take up a subject, you get past Mount Stupid a lot quicker when there's someone to push you tumbling off the top (or at least point out your vast ignorance). It also builds up a reflex for noticing your ignorance - you start to know what it feels like to have a shallow understanding of something and you start to recognize when you're speaking out of your depth. You'll have been conditioned by having been called out in the past. Of course, you're still going to shout from high atop Mount Stupid a lot, but you'll realize what you're doing much more easily.
Caveat: I might still be atop Mount Stupid's Mount Stupid, don't forget that.
A little knowledge is a dangerous thing, not sure what the official name for this particular cognitive bias is (feel free to enlighten me). Probably most of us can recognize that feeling of enlightenment after learning a bit of something new and exciting, and not realizing yet how far it is from the mastery of the subject. I suspect that learning the LW brand of rationality is one of those. (Incidentally, if the words "LW brand of rationality" irked you, because you think that there is only one true rationality, consider how close you might be to that particular summit of Mt. Stupid.) See also the last bullet point in the linked comic strip.
As an exercise in rationality, I suggest people post personal accounts of successfully traversing Mt.Stupid, or maybe getting stuck there forever, never to be heard from again. Did you find any of the techniques described in the sequences useful to overcome this bias, beyond the obvious of continuing to learn more about the topic in question? Did you manage to avoid turning Mt.Stupid into the Loggerhead range?
My example: I thought I was great at programming fresh out of college, and ready to dispense my newly found wisdom. Boy, oh boy, was I ever wrong. And then it happened again when I learned some more of the subject on the job...