Been a consultant, not a contractor, for many years. You cannot be a consultant without reading Weinberg:

"The Secrets of Consulting: A Guide to Giving and Getting Advice Successfully"

https://www.amazon.com/Secrets-Consulting-Giving-Getting-Suc...

"More Secrets of Consulting: The Consultant's Tool Kit"

"https://www.amazon.com/More-Secrets-Consulting-Consultants-T..."

These books kept my sanity and showed me the Universe twisted sense, twisted...But nonetheless a sense.