&gt; &gt; When it comes to maintaining and evolving these systems, the lack of explicit static typing becomes a bottleneck.<p>&gt; Assertion without evidence.<p>...<p>&gt; The typing is in your head, where it doesn&#x27;t get in the way.<p>That&#x27;s fine, if it&#x27;s <i>you</i> working on <i>your code</i> (and it hasn&#x27;t been too long since you last worked on it).  But if <i>I</i> wrote the code, now the types are in <i>my head</i>.  Sure, it doesn&#x27;t get in <i>your</i> way there, but it also gives you no protection against you doing something that completely violates the type assumptions of my code.<p><i>That&#x27;s</i> where the lack of static typing becomes a bottleneck to maintaining and evolving these systems - when the code was written multiple years ago by multiple parties other than yourself.