Thinking clearly
Books commenters say helped them think more clearly, decide better or focus.
Books several people mention
Ranked by how many different people say it helped. Small numbers, so the order is a hint.

A system for organizing tasks and commitments to reduce stress and get more done.
Of course I got his book, and of course it changed my thinking. I wouldn't be writing this if it hadn't. I have ADD, and am also deeply suspicious of self-help literature.

How intuition and deliberate reasoning shape our decisions, and where our judgment goes wrong.
Now I'm deliberately conscious about the decisions I take and retrace my thought process multiple times just to make sure that I haven't fallen pray to some of the cognitive biases.

Why focused, distraction-free work is valuable, and how to train yourself to do it.
I’ve greatly benefited from the tactics espoused by Cal Newport in his book “Deep Work” and in his podcast. I now plan my days (regardless of whether it goes according to plan), have startup and shutdown rituals

A framework for building good habits and breaking bad ones through tiny daily changes.
These ideas totally impacted the way I operate and helped me achieve a lot more than I would have on my own. But I needed to read the book to implement these tactics.

Strategies to overcome procrastination and get work done with less anxiety and stress.
The Now Habit by Neil Fiore offers tools to overcome procrastination and start tasks. It helped me understand my resistance and find ways to move forward.

A guide to overcoming procrastination and inner resistance to start and finish creative work.
After reading the book i was able to convince myself that this was just a resistance and if i wanted to be happy and successful, i would have to overcome this resistance.

A guide to reading nonfiction and classic works more thoroughly and with better understanding.
Ever since reading that book, I've gotten into the habit of writing a summary of each thing that I read. It really forces you to confront whether or not you "got" the point

A father-son motorcycle road trip that becomes a philosophical exploration of quality and how to live.
Helped me understand the dual ways I was reacting to the world - rationally and emotionally - and why I was confused about how to understand and evaluate my experiences.

An introduction to understanding complex systems, feedback loops, and how they shape society and organizations.
I read it once a year. It changed how i think about everything. My career is based on this book. My interaction with people and groups of people is based on this book.

How rare, unpredictable events shape history and everyday life, and why we underestimate them.
Whenever, I see a straigh-forward "explanation", alarm goes off inside mind- 'this is too simplistic, and thus oversimplified, and not entirely correct'.