Street Fighter 4 may only be number 29 in our list of the best 100 games of all time, but if this were a list of the greatest individual video game mechanics of all time it'd be jostling for top spot. To my mind, the best mechanics are multi-functional, designed to be useful in so many different situations that they become the most important component part of the game as a whole. One basic example is Mario's jump - used to cross gaps, to climb onto high ledges, and to attack enemies. One of the true greats is the Dark Souls stamina bar, used for all the important bits of your moveset - running, jumping, dodging, attacking and blocking. But the very best of the lot, to my mind, is Street Fighter 4's Focus Attack. Enormously versatile yet simple to use and understand, it is the key factor in this very special game's success.

This single move, performed by simply pressing, and holding, medium punch and medium kick at the same time, can be used in just about every situation you might find yourself in during a Street Fighter 4 match. It does everything, thanks to three key properties. While the move is charging up, it can absorb a single hit from an enemy attack. On offense, it can be used to cancel a move as soon as it connects. Most importantly of all, you can dash out of it, instantly cancelling the animation whenever you want.

Struggling to find a way around an opponent's fireball game? Use the Focus Attack to absorb a projectile, and dash in to punish your foe before they can recover. Someone jumping at you and you're not sure which way to block? Focus to absorb the hit and dash to safety. On defence, it's a vital escape tool. On the attack it is a transformative addition to a well-worn mechanical formula, used not only for extending combos, but also saving your skin after you make a mistake. Throw out an ill-advised dragon punch, for example, and you can make it safe by Focus cancelling and dashing away. It's great during the neutral game too, used to intimidate and bait mistakes.

At first, all I ever did with it was just hold down the buttons in the hope of landing a lucky, fully charged Focus Attack on an opponent, since it does a hefty chunk of damage and makes them crumple them to the floor, which looks pretty cool. But as my understanding of the move's various abilities grew, so did my understanding of - and ability at - the game as a whole.

This has always been the secret to Street Fighter's success; it is perfectly playable and, seemingly, fully understandable at even a beginner level. The more you play, the more you understand, and the better you get at it. Street Fighter 4 is only as complex, as difficult, as you want it to be. But if you want to get better at it you're going to need to Focus.

It says a lot, I think, that across seven years, multiple iterations and several balance patches, Capcom hasn't touched the Focus Attack. New characters have arrived, new mechanics worked into the battle system, and existing ones tweaked and refined, but that remarkable two-button move is so vital to the rhythm, the flexibility, the brilliance of the game as a whole that you just can't touch it.

Which is not to say that Capcom hasn't had work to do elsewhere. Looking back now, the original Street Fighter 4 was a little broken; damage output was insane, character balance was all over the place, and there were infinite combos. Since then, Capcom has tinkered endlessly, if rather slowly - there are few other game companies with the brass neck to announce a balance patch, give it a name, and make you wait six months for it - but Ultra SF4, seemingly the final version of the game, now Street Fighter 5's on the way, is pretty much faultless.

Taken in isolation, it's no great surprise that the company that defined the fighting game with Street Fighter 2 should be the one to redefine it years down the line. But it's the context of the thing that really strikes me. Before SF4, fighting games were dead, the sole preserve of a no doubt passionate, but rather small, community. Now that community is so large and so global that Capcom has just announced a worldwide eSports championship with a $500,000 prize pool. And just as Street Fighter 2's success spawned a host of imitators, so has SF4 sparked a revival in the genre as a whole. Fighting games are back on the map, and once again, it's all thanks to Capcom - and specifically to the Focus Attack, that magical, multipurpose two-button move, the beating heart of the finest fighting game of all time.