First of all it has to be noted that no shot is based on itself. For example take Tarek Momen and his famous attacking boasts - they wouldn't be as efficient as they are if his length game wouldn't be as solid and powerful as it is. Due to the latter, his opponents stand further back on the 'T', and this is why he can go more often than other players for the attacking boast option. Of course, another question is how Tarek executes his attacking boasts technically, but be assured that the fact that he knows that his opponents stand further back and in addition can't really read his intentions allow him to go for this shot in a mentally relaxed manner. And being relaxed - whilst being committed and concentrated of course - is a key factor in order to chose the right shot and execute it in the right way.
The same applies to Ramy Ashour's famous backhand volley nick. Of course, Ramy has spent hours and hours practising this shot in order to memorize the possible geometries of it, but observe how often he plays - instead of the volley nick - a powerful and deep cross-court (0:39) or straight (0:44) backhand volley. Again he goes for these options to create uncertainty in his opponent's mind. In the case of the straight deep volley at 0:44, Willstrop basically expects the redoubtable volley nick attempt and goes therefore the wrong way; but instead of the cross-court nick the ball was sent this time straight deep; okay, Ramy finds the nick even when he hits straight as this ball was just perfectly dying first in the sidewall then in the backwall nick, there was nothing James could have done, but even with a less perfect shot, James would have been late to react as he went the wrong way - not to mention that in the future he will be even more uncertain what to expect from Ramy in that position when the ball comes shoulder height around the service box: the nick attempt or the deep straight version.
Having said all that, I would also like to say that what Ramy is doing with the volley-nick is neither non-sense nor magic. It's a logical shot, deeply rooted in the nature, in the geometrics of the game, that I believe, in the near future, will be considered almost a basic shot, just like the straight drive. Ramy was the first in the history of squash to take this shot option seriously and to apply it systematically first into his training regime from early junior age and then as a next step into his game; as such he really deserves to be considered revolutionary. From now onwards, I think, no coach in the world can afford not to integrate diverse volley-nick routines into their juniors training program. As a minimum, five to ten minutes at the end of every training session, get your opponent to feed you and then return the favour. Believe me, you train this shot and it will come; maybe not as often and as well as for Ramy, because he has been busy with this for a decade and a half, but within a month or two you will see the difference.