Okay, okay … Zipf and Pareto were sitting at a bar, and this lizard walks up to the bartender, and the bartender says ‘Why the long tail?’.
HA ha haa haaaaa!
Okay, now that’s out of our systems … Zipf, Pareto and the lizard actually have some very important and scientific things to teach us about internet marketing and SEO! Here’s why you should be familiar with all of them (enough to recognise any if they walked into the bar where you were sitting), for your own SEO benefit 
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1. Zipf’s Law
This law states that the specificity of any word is inversely proportional to the number of times it will be used in any context. Words which are broader and more generally applicable will be used more times than narrower words, and vice versa. The narrowness of usage is obviously compounded when you make the ‘word’ into several words, or a phrase.
Obviously, this tells us that the broader your keywords are, the more people will be searching on them. There is an enormous caveat, though … this also means there is many more websites to compete with for the rankings and traffic.
2. Pareto’s Principle
You have probably encountered this in some other form – Pareto is the ‘father’ of the 80/20 concept, or the idea that 80% of results come from 20% of the activity.
You know that you wear 20% of the clothes in your wardrobe 80% of the time … but in SEO terms, Pareto’s principle means that 80% of your profits will come from 20% of your visitors, that 80% of your visitors will come from 20% of your keyphrases … etc. In practical terms, how should you account for that? By paying attention to that 20% that generates results, and aiming to expand those areas … aiming to break the ‘law’, in other words!
3. The Lizard
You might have heard of long-tail search queries before, but not many people realise that the ‘long tail’ actually belongs to a lizard. If you graphed out the search queries on a given topic (credit checks, for example), with the most frequently used and clicked-on keywords at the left hand side of the graph near the axis, and the least frequently searched keyphrases tailing off towards the end, you’d find that in the entire conceptual environment, the head is very short and broad … and the ‘tail’ of less frequently used (but more specific, according to Zipf’s Law) keyphrases actually make up a sizeable portion of the searches.
Focus on the long tail!
What’s more, these long tail search queries usually lead to much better sales:visitor ratios, because a specific keyword is more ‘targeted’ to your website, meaning that your business is more likely to be what the customer is looking for!