Remember the 80-20 Rule? Also known as the Pareto Principle, it's the idea that in almost any field, business or undertaking, very few causes (roughly 20%) are responsible for a great disproportion (80%) of the results.

For instance, your best 20% of customers may be responsible for 80% of your sales. Or 20% of your products may generate 80% of the factory defects. Or the richest 20% of a population own 80% of the wealth. The phenomenon has been observed in many different fields, from economics to science to pop culture.

That all started changing, at least for online retailers, when Chris Anderson published his great book The Long Tail. In it, Anderson described a new world where online merchants needn't limit their inventory to only the top-selling few items, but can carry (through electronic distribution, drop-shipping, just-in-time manfacture, and online retailing), a virtually limitless supply of even the thinnest-selling products. The transformation is seen most clearly in the massive inventories of Amazon, Netflix, and iTunes -- much larger than any traditional seller of books, DVDs or music could ever offer.

In this envronment, Anderson sees an inversion of the 80-20 principle, where the "hits" (the very fer bestsellers in the head of a sales curve) are outnumbered in terms of sheer volume, by the "misses" (all the obscure niche products in the tail).

This view has been embraced by search-engine optimizers and marketers, who recognize that the larger a "keyword universe" they target, the more specific and high-converting those searches become. Very specific, multi-word "long tail terms" are in vogue and make up a big part of most search marketing programs today.

But recently, on his blog and on DM News, Lance Neuhauser offered a new take on the subject. He reminds us that search marketing takes time and is still a fairly thoughtful and manual process. If you factor in the key elements of time, money and effort, search marketers should renew their attention to the 80-20 rule. Going after the head terms, says Neuhauser, is the best use of our time and the fastest way to move the needle. Or as he puts it search marketers "need to properly prioritize our efforts to make the greatest impact on our goals."