"I've read somewhere that soft skills are more critical than technical skills for business success."
I've learned not to believe everything I read.
I have a degree in Psychology, which is my way of saying that I've read an almost stupid amount of books related to interpersonal relations, group dynamics, people-stuff-in-general.
The Math parts of my degree and my graduate-level training in Statistics and Operations Research led me to read a crazy amount of material related to Project Management and Decision Theory.
That said, for me, the most important career-development ideas were those that made me more mindfully masterful of my tradecraft. So, the best for me was The Pragmatic Programmer: From Journeyman to Master. I note that I have never aspired to management. I wanted to be the most guru-ful developer - senior project analyst/engineer or team lead maybe, but not non-coding manager.
How you define "success" depends on your goals.