Everyone does not have the right to have his opinion taken seriously.  In order to have an opinion about something that should be taken seriously, for example, it is a necessary condition that you understand the thing about which you are going to express an opinion.

For example, I have had people often tell me that they disagree with AlbertEinstein's Special Theory of Relativity ... (I might add that I'm none too happy about it myself) -- on investigation, I found that they didn't even understand it.  They were just repeating something they had read in a popularization or expressing a conclusion to which they had jumped.  Their opinion is not data about the theory's rightness or wrongness.  It is data about their psychology or state of belief ... another matter.

Consider the Source means -- only take opinions seriously that are informed.  Uninformed opinions are only statements about the psychological state of the opinion holder -- which may be important in some contexts. --RaySchneider

Especially beware when a person who is expert in one domain holds forth on another domain in which he or she is not an expert. -- DaveHarris

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I generally disagree with this -- you have to weigh each opinion separately.  An OutsideObserver can often see things in a problem that "Experts" don't because they CantSeeTheForestForTheTrees. For a great example, see the book "Longitude" by DavaSobel (http://www.amazon.com/exec/obidos/ASIN/0140258795/o/qid=933253784/sr=8-1/002-2271998-4412034).  It talks about how an outsider (to the scientific establishment) solved the biggest technical problem of the time by NOT doing what the established experts did and sticking to his guns when he knew what he was doing was correct.  --KyleBrown

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This is all well and good as a philosophy ''if and only if'' you know enough about the source to know how well informed they are.
Consider 'Just because I don't know C++, doesn't mean I have nothing to offer to this design', or 'Why do management never listen to their employees?'.
If ConsiderTheSource were a universally applicable maxim, anonymous suggestion schemes would never work, and yet they seem to. --FrankCarver

ConsiderTheSource is better known under another name: the AdHominem fallacy.  When you're delegating cognition to someone else--that is, depending second-hand on someone else's ideas, like when you visit a doctor--then ConsiderTheSource makes sense.  It can also make sense when deciding which ideas to spend time exploring.  But it's a fallacy of relevance when evaluating ideas first-hand.  --BenKovitz

SetTheBozoBit is another way to ConsiderTheSource, which could be formulated as "tend to be suspicious of anything someone says if they have been proved seriously mistaken before". It's probably more widely applicable than the interpretation above, i.e. "only trust someone who's a known SourceOfGoodBits in the problem domain".

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See also AdHominem, SetTheBozoBit, ConsiderTheIdea.