Think and grow rich - Napoleon Hill
That last one made something click in my head but I find it hard to describe what it is exactly. The key concepts that I learned from this book are in my thoughts and actions every single day.
Some may consider the book and its ideologies excessively materialistic, but I personally find that outlook refreshing especially considering the subject matter: making money; furthermore I think that take is a little baseless as the viewpoint on willpower etc. that Napoleon Hill provides can apply to far more than just accumulating wealth if utilized correctly.
All in all though, it was easily one of the most life-changing books I've ever read and I'm glad to see it's affected others positively too, cheers!
The simple lesson of trying to look at things from other people's perspective is absolutely invaluable.
Also, Cryptonomicon was an unexpected eye-opener on how every privacy-oriented tech will be instantly abused by people you'd never want to have it in the first place. Cypherpunk has a flip side and it's pretty damn dark.
Apparently he was a bit of a fraud. Or generously put... a fake it till you make it guy. I don't think this is an ad hominem attack, as credibility matters in this case.
The Untold Truth of Napoleon Hill - History's Most Beloved Con-Man