INTs are closest to the word INTelligent. Coincidence? Yes... it is. The stereotype of INTJ intellect would have derived from the obsessive nature of many INTJs trying to prove they are smarter than everyone else. A type obsessed with intellect and that is why they are associated with it. It does not however mean they have it.
I agree, and would like to add that a type obsessed with it would more likely than not be trying to improve upon things most of the time, or at least often.
Not saying one would have to be an INTJ to be intelligent or insightful, though, that'd be stupid.
All MBTI types have assigned roles, sort of. The INTJ one is given.
We amass and process knowledge. Some are genuinely retarded, though.
I know quite a few "INTJs" with disorders and others who are just plain rude/unpleasant.
Some i've seen, on here in particular, fall into the anti-social category.
I'd say that the chance of failure during construction of an INTJ is high... Well, any NT type, to be honest.
But, in the cases where the INTJ isn't a completely flawed construction, things might work out well and you get an individual who will be a lifelong active learner.
As for myself, I know I have my flaws. Temper, gluttony, competitiveness...
But, I am overcoming them and evolving, gradually.