Learning new languages makes you a better programmer. It really has very little to do with C or Lisp specifically.<p>The more different the language you are learning is from ones you have used in the past, the more new approaches you learn. For instance if you already know C++, you'll learn a lot less from learning Java than you would if you learned Lisp (or ML, or Haskell, or Smalltalk) - purely because the delta is much larger. Similarly, if you already knew Ruby you'd probably learn fewer new techniques learning Smalltalk than Haskell, and if you already grok Scheme you'll learn very little from Common Lisp.<p>If you are a C hacker, and especially if C is your first and primary language, Lisp just happens to be on the far other side of the wheel of languages, so you'll learn a heck of a lot from it. I would wager that learning C would make a Lisp hacker better at Lisp, too, though I don't know anyone for whom Lisp was a first language.