Physically Based Rendering: From Theory to Implementation, Third Edition, describes both the mathematical theory behind …
[Just as] other information should be available to those who want to learn and understand, program source code is the only means for programmers to learn the art from the predecessors. It would be unthinkable for playwrights to read their plays [or to allow them] at theater performances where they would be barred from taking notes. Likewise, any good author is well read, as every child who learns to write will read hundreds of times more than [they write]. Programmers, however, are expected to invent the alphabet and learn to write long novels all on their own. Programming cannot grow and learn unless the next generation of programmers has access to the knowledge and information gathered by other programmers before them.
-Erik Naggum
— Physically Based Rendering, Third Edition by Matt Pharr, Wenzel Jakob, Greg Humphreys (Page 1)
This is the opening quote of the preface; the very first thing anyone who reads this sees. This is also one of the most accurate statements in existence about the expectations of programmers, engineers, and developers. As an engineer, it's so frustrating to not always be able to share my learnings, research, and knowledge with others in my field because of the commercialization of software. This quote is a tour de force commenting on the reality of the modern software industry