CelticDeath posted that the key to tactical sucess lies within these three:
visualization, calculation, and pattern recognition - You need to master all three to become a tactical whiz. I agree with him, and since I have nothing better to do, Let me expound on my thinking regarding the matter.

"The tripod is the most unstable of all devices". This dictum is true. Weaken one leg and the whole structure collapses. And so, it goes without saying that being weak in one of the area above, significantly lessens our tactical abilities. Let us examine each one of these legs in detail.

1. Pattern Recognition - This is defined easily enough. A corridor mate, a pawn fork, all the tactical tricks in the book. All of them, no matter how difficult a combination, resolves into distinct simple patterns. The way geometry formulas resolves into simple additions. In an alternative way, we can think of them as tactical ideas. And these patterns, these ideas are what makes combinations works

"At the heart of every combination there shines an idea, and though combinations are without number, the number of ideas is limited"

These patterns must be memorized to reach mastery. We must know it the way we know our name. But the question that should now cross our minds is - when we see a pattern, is it really wise to iniatite a combination based sorely on it? For example, when an opponent makes a move and we instantly recognize that he placed his piece in a forking square, do we launch the fork? If it was a patzer, perhaps we would. But I have learned, and much to my sorrow, that most of the time I should not. Particularly, when a computer makes such a move, it usually is a deep trap.
There simply is no way to tell without looking deep enough to know. We have to always look, always verify things. Our opponent is no fool. He must have known that is a forking square. Or did he? how can we be sure? And so this brings us to -

2. Calculation - This is the second component of tactical mastery. The great safety net. This tells us if a move was a trap or a simple blunder. And because initiating combinations and sacrifices always entails risks. Good calculating techniques are needed to mollify it somewhat. I mean, there is really no risks if all possible replies of the opponent was worked-out beforehand. Then we say, ah! the combination was sound. A queen was sacrificed true, but only temporarily as can be seen in the variation Bxe5, fxe5, etc. etc..

But calculating very deep combinations requires that we see the position clearly in our head. A small mistake could nullify a perfectly good variation

3. Visualization - This brings us to the third component of tactical mastery. Having perfect sight of future eventualities in the board allows us to trust our calculation. If calculation is the safety net of pattern recognition, visualisation is the safety net of calculation. The limiting factor on how far we can calculate effectively. Because when we say we can calculate up to ten moves, what we really mean is that after ten moves, the position is still solid enough in our head to understand it. If the image becomes fuzzy, calculating any further is useless.

Having very great strenght on all three is the pre-requisite to becoming a deadly tactical chess master. Most class player would probably say "I am already very good at tactics". And they are partly right since they have tons of memorized patterns already stored. Only partly because most class players are like that (me included). Very strong in patterns, but not enough calculation and visualization. I say not enough because the more important question is not if we saw a tactic but, when did you see the tactic? If you saw it when it is already at the board. Good for you. But that is not the deadly tactical chess master. Thats just doing what every Tom, Dick, and Harry does. And so we are not interested in it. When we start to see the tactics, a couple of moves before it is there, then I think that is the start of tactical mastery. That is what we are interested in. A tactical master sees tactics before the opponents do. He reads the position with his eyes closed. And after the combination is consummated, he tells them in his mind:

"Young fool. Only now you see. Only now you understand. You have paid the price for your lack of vision!"