In university, I learned Perl out of curiousity. It was the first scripting language I tried; I was only familiar with Java, C and Scheme at the time.
After reading Programming Perl from cover-to-cover, I suddenly felt like I had superpowers. I probably would have felt the same if I'd taken the time to learn bash scripting, but that's not how it worked out.
I tried to automate everything in my life with Perl. I'd walk to class in the morning and a script had already scraped and downloaded my lecture materials and sent a print job for me. It emailed me if it couldn't find notes for one of my scheduled classes. Others would manage my assignment submissions. I wrote scrapers to detect what events on campus might offer free food.
This was the first time I felt like I could write programs that actually had the power to improve my life. It changed my perspective on what I had the power to do as a programmer. I'll always be grateful to Perl for that.
I also learned how to quickly develop a thick programmer skin by asking questions on comp.lang.perl, but that's another topic altogether.