So much depends on opening theory?

Kasparov On The Openings

"By the time a player becomes a Grandmaster, almost all of his training time is dedicated to work on this first phase. The opening is the only phase that holds out the potential for true creativity and doing something entirely new." - G. Kasparov

“How much book do I need to know?"...

        "The bare minimum is: You need to know the traps that come up in your openings!” – GM Andrew Soltis 

It is important to study the openings and know what traps and disasters may arise from a particular variation, either to use it against an opponent or avoid falling for it. Opening traps are useful in blitz, online play, and usually with players who do not study opening theory.  

Naturally, even Grandmasters are not exempted against making gross blunders. Many strong GMs get caught in a trap, and we can all agree that what happens to strong players can turn up in anyone’s games. You just have to remember at one time or another, chess players from amateur to Grandmaster have fallen for a devious trap or employ a crafty hidden idea to unsuspecting opponent.

        (I won't spoil the surprise, but on my next blog i will show some of my personal  favorites about catastrophe in the opening.)

This is a must-have!! 
If you want to advance your opening play to the level of Masters/Grandmasters, you should learn the general principles of opening play and have a powerful opening repertoire. Also know the secrets of proper and efficient opening preparation at a very high level.
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Link >> GM Opening Laboratory 2

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Another KEY part of the chess course is the "Practical Part". 

        It will help you train the SKILLS, during the course’s study. Thus you’ll be able to implement it in your practical games. You will complete some special training to become a real expert in these openings, and be familiar with all of the specific variations,as well as their typical ideas and plans.

                      (The images and links will bring you to RCA's Chess Course overview.)