From Peter Norvig's "teach Yourself Programming in 10 years"
"Learn at least a half dozen programming languages. Include one language that supports class abstractions (like Java or C++), one that supports functional abstraction (like Lisp or ML), one that supports syntactic abstraction (like Lisp), one that supports declarative specifications (like Prolog or C++ templates), one that supports coroutines (like Icon or Scheme), and one that supports parallelism (like Sisal)."
That's actually very similar to the point this writer makes: that learning different languages does have benefits, but that they should be significantly different. The two just differ on whether you should learn many different languages, or a few.
These days, I don't know if I can trust advice on the internet anymore. Could be they just want to send the competition down the wrong path (Norvig is commercial now, working for Google). Follow their advice, and you waste a lot of time, while they are busy making progress.
If you're trying to compete with Norvig right now, for god's sake don't waste time learning more languages. You have a business to build.
If you're willing to bide your time and you hope to develop jedi-level expertise eventually, then I think it's still good advice. But again, it will pay off only in the long term.
Likewise, if someone is beating you up after school every day, don't start studying a martial art that will take you 5 years to learn properly. Learn something quick and dirty. But if you want to learn to be a true master of martial arts, it will be a lifelong study and you will likely need to learn at least several styles.
But, as noted, brass knuckles (or a gun) will not cause you to grow up as a person. The martial arts teach patience and poise, which is almost exactly the opposite of a quick fix.
More concretely, Sig Kufferath (who basically carried the Danzan-Ryu torch to mainland USA) apparently beat the hell out of a couple guys who tried to mug him, then got them medical help and sent them flowers in the hospital. (The story may be apocryphal, but I would not have put it past him) Norvig's motives appear similar -- he is an acknowledged Jedi and has little to fear, in general, from helping others to raise their game. Having crossed paths with both guys, I feel reasonably justified in my perception.
My apologies for drawing Norvig into this - actually I also hold him in high esteem and I don't really think he had any ulterior motives for that remark. And I do like to learn new languages.
HN sometimes makes me think what I wrote, though - a good way for the competition to keep you busy, for example by posting math riddles and stuff.
From Peter Norvig's "teach Yourself Programming in 10 years"
"Learn at least a half dozen programming languages. Include one language that supports class abstractions (like Java or C++), one that supports functional abstraction (like Lisp or ML), one that supports syntactic abstraction (like Lisp), one that supports declarative specifications (like Prolog or C++ templates), one that supports coroutines (like Icon or Scheme), and one that supports parallelism (like Sisal)."