My own experience is that working in typed languages, then going to untyped ones... your sense of types and the problems they address is already fairly high. Your 'untyped' code likely still avoids a lot of the problems you might otherwise encounter, just because of whatever habits you may have picked up in the typed system. Going the other way - untyped to typed - tends to present a lot of ... tough moments along the way, because you're having to put a lot more thought about things that you didn't have to before.