> In the real world, picking up a new language takes a few weeks of effort and after 6 to 12 months nobody will ever notice you haven’t been doing that one for your entire career.

Spoken as someone who has never taken the time to fully master a programming language and, from the sound of it, has never worked with someone who has either. The difference between someone who has spent 6-12 months with a language compared someone who has spent 6-12 years is night and day. From the general tone of the article, he obviously focuses more on the business value than on the technical side and that is a pretty good approach for making money. But I'll take Peter Norvig's advice (http://norvig.com/21-days.html) over this guys when it comes to mastering a language.

To be fair most of the content of those articles is pretty decent though and it is just a pet peeve of mine when people claim that mastery of your medium doesn't matter.