What Book(s) changed your views

[Chris Davidson]

I want to know what book or books that aren't commonly talked about helped change how you view investing, or real estate. I started reading the Rich Dad series before I got started, but when I read What Every Real Estate Investor Needs to Know about Cash Flow... And 36 other Key Financial Measures it helped me see there wasn't some secret formula or hard calculations going on to get the deals it was just math and helped remove emotion from the investing side. There have been many more that have helped me narrow my focus and ones that have also helped me open my eyes and see more possibilities. 

Interested to hear what book(s) helped change your views.