One very simple and significant cost is developer time. It simply takes less time to write code in a dynamically-typed language. You don't have a compiler to pl

One very simple and significant cost is developer time. It simply takes less time to write code in a dynamically-typed language. You don't have a compiler to please, you don't write extra code to massage types, annotate types, etc, and most dynamically typed languages are pretty elegant (i.e. Clojure), where you can pack a lot of punch in just a few characters. So the trade off is: static typing gives you more compile-time certainty, but at a cost of spending more time developing your code. Dynamic typing gets you to a working product or prototype typically much much faster, but with added run-time debugging. Each has its benefits and costs. In my experience, there is no doubt that dynamically typed languages are faster-to-production than statically-typed. This doesn't mean that I don't admire static typing, though, because most developers appreciate some degree of purity in their work.