Speaking of "groking", Stranger in a Strange Land, Time Enough for Love and The Fountain Head have probably had the most impact on my mindset.
Each book is rather different, but in general the idea of all three is
> You have to be in life for yourself, and only you can define who you are / want to be.
That doesn't necessarily mean you need to be mean, but the idea that "greed is good", or that it's okay to be selfish, provided you think long term. It's about coming to terms and accepting you are greedy. But with that insight you can do introspection and learn about what drives you and make decisions yourself.
It's almost as if another layer of consciousness, learning about ones self.