I am not sure this article gets it quite right. Yes, there are a lot frameworks that help shield the developer from having to deal multi-threading concerns. H

I am not sure this article gets it quite right. Yes, there are a lot frameworks that help shield the developer from having to deal multi-threading concerns. However, so long as you have shared state, you still need to worry about the problem. Let's take the example of a web application, be it in PHP, Java, etc.: What happens if your user has multiple browser tabs open to your application and submits concurrent requests that modify the user's session? With multiple cores, it is much more likely that the concurrency bugs in your application will be exposed. Languages like Clojure help you explicitly reason about shared mutable state.