Languages and frameworks are tools, but they're tools that require significant time investment to master and there are too many of them to master every one. Th

Languages and frameworks are tools, but they're tools that require significant time investment to master and there are too many of them to master every one. There are many, many cases in which a given person's "optimal" language to use for the task is different than the "optimal" language would be if the user were somehow equally skilled in all. Obviously, if the project is far outside the sweet spot of a given programmer's favorite language, it's worth it to learn a different one. The larger the project, the more often this is true. If for example, a Java specialist wanted to build a webapp, it would likely be worth it to invest the effort to learn how to do so with JavaScript instead of sticking to the familiar GWT. But for a smallish text manipulation task, it's just not worth it for an expert user of Ruby (a pretty good text manipulation language) to learn Perl (a language really designed for text manipulation). The sweet spot, in my opinion is to work at getting very good at one language per major domain area and change focus only for large projects, for projects far from the sweet spot of any already known languages or for fun.