I spent years knowing nothing but C and I’d say it handicapped me in many ways. (I recall insisting that it would be impossible to do anything without assignment.)

After getting my eyes opened a little bit, I read SICP and it was mind blowing. I read a little Haskell, wrote a little Clojure and a lot of Scala. And even though the day job now is Java and Python, I’m much better off for having bothered to learn it.