In school, I had a really boring stats class right after my OSes class and my buddy and I used to skip it and sit in the labs and code up CGI scripts. My school didn't teach Perl (or any other scripting language), but in our minds CGI==Perl, so we Googled and "learned Perl" from those sites that people now caution others about on the Monestary.
That summer, knowing Perl got me my first internship at a big company, where I was introduced the the Perl Bible. I read it practically cover-to-cover over the course of that job and that was really "learning Perl".
Sometime during the course of that job I discovered perlmonks and that was the first time I really started to understand the scope of Perl.
That new Perl knowledge led to a second internship, followed by a first real job, then a second. And along the way I never really stopped learning, with each job bringing new areas of the language to explore.
So really, skipping class (to learn Perl) has been the gift that keeps on giving.