What's your reply to your comment's siblings, then?
They're being too literal. David_Gerard's comment is an aphorism that, like all good aphorisms, is easily expressed and contains a kernel of truth. Think of any personality descriptor: ambitious, introspective, thoughtful, analytic, romantic, idealistic - they are all both strengths in some situations and weaknesses in others.
On Quora: What are some stupid things smart people do? Examples of common types of stupidity that are typical of otherwise very smart people.
Lee Semel's answer in particular would make a great post here: a "to don't" list. You may wish to go through and identify the cognitive bias or biases each is an example of.