Some commenters seem to think the only reason to learn a bunch of languages is to have a bunch of tools ready to apply to whatever problem comes along next, and

Some commenters seem to think the only reason to learn a bunch of languages is to have a bunch of tools ready to apply to whatever problem comes along next, and yes, it is difficult to know many languages well enough to do that. However, I think they're missing the point of this blog post: dabbling in a bunch of significantly different languages makes you aware of the limitations of the (smaller set of) languages you use heavily enough to count as "ready to apply."