For some unfortunate souls SEO is simply learning of tricks and techniques that, according to their understanding, should propel their site into top rankings on major search engines. This understanding of way SEO works can be effective for a time however it contains one basic flaw ... rules change. Search engines are in a constant state of evolution in order to keep up with SEO's in much same way that Norton, McAfee, AVG or any of other anti-virus software companies are constantly trying to keep up with virus writers.
Basing your entire websites future on one simple set of rules (read: tricks) about how search engines will rank your site contains an additional flaw, there are more factors being considered than any SEO is aware of and can confirm. That's right, I will freely admit that there are factors at work that I may not be aware of and even those that I am aware of I cannot with 100% accuracy give you exact weight they are given in overall algorithm. Even if I could, algorithm would change a few weeks later and what's more, hold your hats for this one; there is more than one search engine.
So if we cannot base our optimization on a set of hard-and-fast rules what can we do? The key my friends, is not to understand tricks but rather what they accomplish. Reflecting back on my high school math teach Mr. Barry Nicholl I recall a silly story that had a great impact. One weekend he had entire class watch Dumbo The Flying Elephant (there was actually going to be a question about it on our test). Why? The lesson we were to get from it is that formulas (like tricks) are feather in story. They are unnecessary and yet we hold on to them in false belief that it is feather that works and not logic. Indeed, tricks and techniques are not what works but rather logic they follow and that is their shortcoming.
And So What Is Necessary?
To rank a website highly and keep it ranking over time one must optimize it with one primary understanding, that a search engine is a living thing. Obviously this is not to say that search engines have brains, I will leave those tales to Orson Scott Card and other science fiction writers, however their very nature results in a lifelike being with far more storage capacity.
If we consider for a moment how a search engine functions; it goes out into world, follows road signs and paths to get where it's going, and collects all of information in its path. From this point, information is sent back to a group of servers where algorithms are applied in order to determine importance of specific documents. How are these algorithms generated? They are created by human beings who have a great deal of experience in understanding fundamentals of Internet and documents it contains and who also have capacity to learn from their mistakes, and update algorithms accordingly. Essentially we have an entity that collects data, stores it, and then sorts through it to determine what's important which it's happy to share with others and what's unimportant which it keeps tucked away.
So Let's Break It Down ...
To gain a true understanding of what a search engine is, it's simple enough to compare it to human anatomy as, though not breathing, it contains many of same core functions required for life. And these are:
The Lungs & Other Vital Organs - The lungs of a search engine and indeed vast majority of vital organs are contained within datacenters in which they are housed. Be it in form of power, Internet connectivity, etc. As with human body, we do not generally consider these important in defining who we are, however we're certainly grateful to have them and need them all to function properly.
The Arms & Legs - Think of links from engine itself as arms and legs. These are vehicles by which we get where we need to go and retrieve what needs to be accessed. While we don't commonly think of these as functions when we're considering SEO these are purpose of entire thing. Much as human body is designed primarily to keep you mobile and able to access other things, so too is entire search engine designed primarily to access outside world.
The Eyes - The eyes of search engine are spiders (AKA robots or crawlers). These are 1s and 0s that search engines send out over Internet to retrieve documents. In case of all major search engines spiders crawl from one page to another following links, as you would look down various paths along your way. Fortunately for spiders they are traveling mainly over fiber optic connections and so their ability to travel at light speed enables them to visit all paths they come across whereas we as mere humans have to be a bit more selective.
The Brain - The brain of a search engine, like human brain, is most complex of its functions and components. The brain must have instinct, must know, and must learn in order to function properly. A search engine (and by search engine we mean natural listings of major engines) must also include these critical three components in order to survive.
The Instinct - The instinct of a search engines is defined in it's core functions, that is crawling of sites and either inability to read specific types of data, or programmed response to ignore files meeting a specific criteria. Even programmed responses become automated by engines and thus fall under category of instinct much same as westernized human instinct to jump from a large spider is learned. An infant would probably watch spider or even eat it meaning this is not an automatic human reaction.
The instinct of a search engines is important to understand however once one understands what can and cannot be read and how spiders will crawl a site this will become instinct for you too and can then safely be stored in "autopilot" part of your brain.