for me it was learning devops

Data Smart, by John Foreman. Out of print, but you can get it from Abe Books: https://www.abebooks.com/book-search/title/data-smart-using-...

Why it is cool?

Because instead of R, Gadoop, Spark, Python, whatever... it started explaining data science with excel.

The best part for me was optimization.

A digital electronics design course I took at the local science museum when I was 11. It was free, so what the heck, I took it on a whim. I didn't know it at the time, but it set the course of my career for the rest of my life even though I'm a software, not electronic, engineer.

Two books I read after 9/11 shaped my path greatly:

1.) Stasi: The Untold Story Of The East German Secret Police

ISBN #: 0813337445

2.) The Rise and Fall of the Third Reich

ISBN #: 9780671728694

Both should be available in most public libraries, but with the ISBN you can usually get almost anything via inter-library loan.

The Boy's Second book of Electronics by Alfred Morgan(1957) introduced me to electronics circa 1975, and lead to a technical mindset and lifestyle.

Not a book or course per say, but based on a book:

The Gervais Principle, Or The Office According to "The Office" by Venkat [0]

Other contenders:

Sapiens by Yuval Noah Harari [1]

Haseeb qureshi's articles on Negotiating [2]

These along with er... mind-altering substances, helped me see that reality as we live it (careers, status, institutions, ect) is like software: built/programmed by humans and can be changed by shifting your perspective.

[0] https://ribbonfarm.com/series/the-gervais-principle/

[1] https://www.youtube.com/watch?v=CGhTQ4iruLc&list=PLfc2WtGuVP...

[2] https://haseebq.com/my-ten-rules-for-negotiating-a-job-offer...

Programming Perl, 1st Ed. from Larry Wall. The three great virtues of a programmer were enlightening for a fresh-outta-college beginner.

"The C Programming Language", by Kernighan and Ritchie.

"The Annotated Turing" - I didn't know you could meaningfully intertwine biography and technical analysis like that.

To answer the question as I misread it:

  What's the most career altering *course of action* you've gone through?

I was an IT guy, and I took a job making gears in a job shop. The pay and commute were horrible, but it was immensely satisfying. Some of the gears I helped make will still be in service in a century.

A/B testing.

I learned how to write high performance JavaScript code directly to the DOM without a bunch of abstraction bullshit. Turns out this proved to be a bias because our experiment code frequently executed faster and failed far less than the actual production code that went out later.

Code: The Hidden Language of Computer Hardware And Software by Charles Petzold.

I read it in my second year of studying computer-science during the summer break, and it completely changed how I view computing.

First of all, the contents alone are quite valuable, even though it is an old book, as it basically walks you through building a simple relay computer on paper, with a CPU, RAM, simplified input devices, teaches you Intel 8080 assembly as an example of assembly programming, and then even goes over a simplified BIOS, OS, GPU and higher-level languages at the end, and it does not assume you have any previous knowledge; it starts from the basic physics behind electricity, then goes into boolean algebra, logic gates, etc. It's basically computer-architecture for the layman.

Beyond the content of the book, I think the biggest mark it left on me is that it taught me that there is no magic behind the layers of abstraction, and that breaking problems and concepts down into simpler ones can make what initially seems like a very complex topic into something that someone can easily follow and understand.

After I read the book, a lot of things I had already learnt at university felt like they made more sense, and I then took courses like Computer Architecture and Digital Circuit Design, where I felt a lot more confident than I probably would have, had I not read that book. It definitely colored how I viewed a lot of the courses I took at university after having read it.

In my career as a software developer, I still often think about that book, and I love to learn things by re-inventing the wheel and building simpler versions of complex existing software.