It's pretty easy to keep grinding more skill and effort. But it can be terrifying to deal with conflict, aggressive people, manipulative clients, competitors, and it can really discourage you along your career. Most people end up avoiding those things and running or hiding from problems. Trying to bring it up with management can often end up with you getting outmanoeuvred.
The book is great because it covers ways to disable threats. Most people are inept in conflict - they just dump more energy at it until they win or run out of energy. The book teaches techniques like counter-attacking, using your opponent's aggression against them, when to be more aggressive, when to be diplomatic, when to retreat, when to hesitate. How to drag an opponent into a long drawn conflict and kill them with attrition. Or how to intimidate them by making them feel trapped. The goal is to resolve and end conflicts quickly, maybe even turn an opponent to your side.
Like martial arts, it would be best to not have to use it. But I've had to several times, especially as an entrepreneur. It's also one of those things that give you enough confidence to handle certain obstacles, opening more doors and more choices that way.