How important is cycling?

Question
I have a very inquisitive nature and experimenting with actions and reactions is always fascinating.  About two months and a half ago I bought a ten gallon tank, and rescued three fish-two black moores and one red fantail- from a fish store which advertises fish expertise and provides substandard, sick fish. Anyways I have one black moore and one red tail left-the one black moore died of many illness which were discovered when I disected him after death-the shop sold me an already sick fish.  

Since then I have treated the tank with salt and they are both healthier. I have just separated the red tail and the remaining black moore.  The red tail was showing signs of stress and lethargy, and since I know it could be due to the over crowding  the tank-it seemed like the best thing to cure her stress.

Well I was right...however I did not cycle the ten gallon the red fin is in.  In fact I have never done a partial water change with any fish I have ever had.  Always full water change with appropriate amount of water conditioner, some salt and left it at that.  

I had a black moore for seven years once in a small five gallon which I only did full water changes with...it was perfectly healthy, turned gold and only died because my little cousin was visiting and poured a lot of vinager into the tank without telling us...needless to say I was not thrilled and to this day have not forgiven them.

So basically my question is how important is cycling a tank?  From my experience it is not a big deal and my fish always seem healthier after a full change-no signs of stress, perfect gill and tail formation-never any shedding or fin rot. So is cycling a myth, or are goldfish really hardy?

Answer
Hi Katie:  Cycling is not a myth and it is very important.  The story appears in between your water changes.  One important fact that appeared in your e-mail was that you have not significantly over crowded your tanks.  Yes the rule of thumb is one goldfish per 10 gallons of water but that is not a stead-fast rule.  So what occurs between your water changes is very important.  The oldest living goldfish in history was 42 years old.  This is important because in a perfectly cycled and a balanced tank the fish are not exposed to abnormal water chemistry issues as they may be in a tank that is not regularly maintained nor cycled.  Those abnormal chemical levels affect the fish in ways we can not see but it is seen in the shortening of their life span.... realizing of course that your 7  year old black moor died of an accident... his death is still a valid point of observation... since his death was technically a water chemistry issue (extreme) the result is the same and more importantly shows the accelerate cause and effect of toxicity in the tank.... dave