If you were building a sandcastle, a type system is like plastic forms in the shape of castle components (walls, towers, etc)... They help you create a better sandcastle...
This article was essentially saying: "You can remove the forms when you are done and your sandcastle will still stand."
Your hands are your mind... you think the types, check the types, and erase them, but do all of it briefly, while playing with that part, and then move away.
Compiled languages are like building a bunch of plaster mold, and then just doing the castle in one step.
Optional typing, or using Any types and casting, is like using molds for a nice foundation, and using your hands to add little bits on top.
This article was essentially saying: "You can remove the forms when you are done and your sandcastle will still stand."