Explicitly declared types are like anchors. They make it harder to change the program to be a different program. In many cases this is good since it tells wheth

Explicitly declared types are like anchors. They make it harder to change the program to be a different program. In many cases this is good since it tells whether a change breaks things or not. But it does add to the "mass" of your program, makes it harder to change its direction. Your declared types are the shared "language" under your program. It is much harder to change the language that what is said in it. Changing the language would actually change the MEANING of what has already been said.