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.