But it's Saturday afternoon, so let's digress. Let's talk rhetoric.
The secret to dealing with these vague but useful nonscientific concepts like "the Pareto Principle" or "Agile software development" or "cloud computing" or "startup company" or "Zen Buddhism" is that you need to approach your essay with a positive attitude. You need to think like an improv comedian: Train yourself to say "yes". An essay about "what the Pareto Principle means to me and how my specific interpretation might be insightful" -- like the one I've just tried to write -- is potentially useful. But an essay on "what I think the Pareto Principle is and why I think it's totally wrong" often leads to an embarrassing place. [1] It's like trying to punch a cloud. No, actually, what it is really like is trying to attack a straw man, because that is what you're going to end up doing. Arguing with yourself is difficult enough; arguing with yourself and losing in a believable fashion is nigh-impossible. [2]
There's a reason why another term for unscientific things is "unfalsifiable". Don't set out to write an essay on "why this unfalsifiable thing is false". You're gonna embarrass yourself.
On the other hand, a brave attempt to falsify the unfalsifiable is an effective form of linkbait. So I take it back everything I just said. Tune in tomorrow for my award-winning essay: "Why there is no such thing as a startup company." ;)
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[1] If you want to argue with a concept like "cloud computing", you will be more convincing if you choose to argue with a specific instantiation of the concept. You can flame Amazon AWS, or you can flame a certain form of client-server architecture, or you can flame the poor security of a specific online backup vendor. All of which is more credible, because these things can argue back.
[2] Though it can be great for a laugh: http://www.youtube.com/watch?v=CH1Dk-rZ1IE
(read the following only if the YouTube link is down: http://en.wikipedia.org/wiki/Colin_%22Bomber%22_Harris_vs_Co... -- this is meant to be physical comedy.)