What usually slows me down about dynamically typed code is you have some variable returned by a function only denoted by var myVariable = myFunction(); and I'm sitting there staring at thinking... "what are the contents of that variable? what properties do I have access to on that object? what can I do with it?"

And figuring that out becomes a massive time suck when that's a constant across an entire code base. Statically typed stuff means I can very quickly find that out even if it's the first time i'm exploring that particular area of the code.