Similar in meaning to AchillesHeel, but often used to label a weakness that is so likely to cause a problem that the flawed system is completely unsuitable for any use.

This term is often used by people (often inappropriately) to quickly dismiss a potential solution.  Further investigation of the system's benefits or analysis of tradeoffs is deemed unnecessary.

Examples of "fatal flaws" of various systems:
* The system has no security.
* It runs on a virtual machine, and EverybodyKnows that virtual machines are too slow.
* It is not based upon an open standard.
* It is not commercially supported.
* It has a SinglePointOfFailure.
* It is not extensible/scalable/reusable/portable.
* It was NotInventedHere!

Fatal flaws generally aren't fatal at all.  Beware when you hear the term used; such judgments are often based upon prejudices and unsupportable beliefs.

''They're often incorrect, too.''

''Of course, it should be pointed out that in many endeavors; finding the optimal solution is not an available option--it takes too long.  Hence, heuristic measures are often employed to reduce the number of options to a smaller subset that can be examined more thoroughly.''

''One popular story in HumanResources lore is the manager with a stack of resumes on his desk, and one position to fill (assume a down economy).  He sorts the resumes into two piles; evens and odds.  When this is done, one of the two piles is then thrown into the garbage, without any of the resumes in the pile being looked at.  Rational?  In one sense, probably not; you could just have thrown out the resume of exactly the person you need for the job.  In another sense, perfectly rational; the manager's time is limited and he simply cannot afford to investigate each resume.  And given a large enough sample; the odds are that he will find a suitable candidate in the resumes he keeps; even if the ''best'' candidate's resume was one thrown into the bin.''

''This anecdote should probably be moved somewhere else.''
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It's all relative. For me, a FatalFlaw is any laptop without a trackpoint mouse. I would go for a 5 year old used laptop over a state of the art laptop if the latter didn't have a trackpoint. Often a FatalFlaw is something of low/medium importance, but when it hits a threshold, becomes overwhelming and critical. Like a GUI. You can have the most amazing killer app, but if the GUI annoyances pass a threshold, people wont use it.