[u:62728335f2]Cognitive dissonance is a psychological phenomenon which refers to the discomfort felt at a discrepancy between what you already know or believe, and new information or interpretation.
Cognitive dissonance is different from the trance language I described earlier, but elena is correct that it is "easier to sneak up on someone who is confused."
In Ericksonian hypnosis (which has been assimilated into NLP) trance language puts the person into hypnosis, then the hypnotist slips in the suggestions. This is not necessarily bad--if you want to make positive changes and you've contracted with a hypnotist to help you make those changes, that's the way the game is played and everybody wins.
The problem with Landmark, as I see it, is that they put you into a trance, input a lot of empowering suggestions and good information, but they also slip in this "You've been transformed, now transform others by bringing them to Landmark" mickey which turns people into these Landmark enrollment robots without them really knowing what happened.
I'm somewhat immune because I've been through est before and I've taken a lot of NLP courses and I've been through other conversion-type experiences since then. But I must say that Landmark is powerful stuff and I'm not surprised that people go crazy for it.