The goal by Goldratt. I read it last year and it completely changed the way I think about work and life. Once I have figured out the goal, the actual goal, not just deliver the project, stuff like speed up the app by 50% not "implement memorization" I realized nobody cares how I achieve the actual goal. It helps that I work with smart people who also understand this. Unless I am adding to the cost massively (like a few million dollars) all solutions are acceptable.

It also helps massively to figure out the goal first, because most of the time the goal is hidden in management speak or cryptic customer feedback due to language barriers or legal ones.