Lately there has been talk about theoretical openings and its importance in determining results. One needs to "profile" an opponent to bring out the right "weapons" to win. Strangely, I believe Fong Yit Ho's profiling of Yeoh Li Tian was well done in capitalising on Black's need to win. Many similar examples in World Championship encounters have used this tactic, eg Lasker - Capablanca 1914, Karpov-Kasparov 24th game 1985 and Kasparov-Karpov Seville 1987. "To win by detaching oneself from winning" is a supreme psychological tactic adapted from Lee Zhong Chang's Thick Black theory. You may wish to read about it from Chu Ching-Ning's book " Thick Face, Black Heart".
I'm not sure about the author's familiarity of the various tools available today, but perhaps he ought to know of 2: ChessBase and Fritz. One is a database that contains games played in history (up till the latest month), the other a computer engine that shows reasonable moves branching from a position.
Every player who takes the trouble to spend hours and hours perfecting his chess should not do without these 2 programs as they can give a realistic forecast of what's to come when preparing for an opponent. However, this is not all that is. If that were true, all top-level GMs would have churned out wins at every opportunity. Such is the wonder and vastness of the game - not everything is predictable.Generally technical knowledge in the other phases of the game (especially endgames) is even more critical as mistakes tend to happen later in the game and good technique is required to bring home the point. No point in losing a game when you're up a Queen for Bishop+Knight right??
As to the GMs recommendation for adopting a complex opening such as the Ruy Lopez as a must-know for every aspiring player, we need to qualify this statement. GMs eat,sleep and breathe chess so they will have the need to spend every living hour understanding the myriad of variations and its possible positions that can lead to a distinct advantage. An opening such as the Ruy Lopez has about 80 years of history in recorded master games, with it its log of good and bad plans that follow every single variation. Learning the Ruy Lopez by studying the latest lines played today simply does the opening injustice. Many of the plans used today are evolved painstakingly from the past, with contributions by every World Champion and top players in their generation.
So before you decide to embark on this route, I would like to recommend a good book that will explain the evolution of this opening and how one should tackle its study.
Though Mark Dvoretsky does not have a high opinion of Alexey Suetin, nonetheless this man has attempted to scholastically categorise the vastness of chess strategical themes and its relation to the opening, middlegame and endgame. In this book, he gives a good approach to anyone who wishes to study the Ruy Lopez systemically by studying good historical games played by the World Champions, some of which have fashioned useful plans and ideas named after them. I urge you to find this book and read it.
The Ruy is heralded as the King of e4 openings, simply because it offers many faceted approaches to competitive play. One can choose to play tactically against it (the Marshall, Schliemann, Open,Riga variations) or positionally (the Steinitz, Zaitsev, Breyer,Berlin,Cozio, Cordel,Bird) and similarly White too has weapons at his disposal to play tactically ( 5 d4) or initiate positionally (the Worrall, d3 systems, the Exchange variations etc). As Black often dictates what variation to play after 3 Bb5 or 3..a6 4 Ba4, plans in such variations can run to as long as move 25 nowadays so if you do not possess a good memory, mastering this opening may prove futile. Sidestepping with the Exchange does not give White an endgame edge, due to discoveries in this century with 5..Qd6 which renders much of Fischer's analysis in his "My 60 memorable games" irrelevant.
Is it true that this is the only path to mastering chess openings?? I would rather think not. As many of us struggle with the constraints of time, family, commitments, are there not other means that we can play chess without adopting the Grandmaster's approach to learning openings? Simply because, we are not Grandmasters who can afford the time. So unless you are ready to relinquish all your other commitments in the effort of being a Grandmaster and nothing else, this path is not for you.
Generally, for non-GM aspirants, I would rather be content to adopt GM Portisch's advice : " Your task in the opening is to reach a reasonably playable middlegame"