Max von Sydow

You cannot study acting in books. Do it, do it, do it. And watch good actors. See what they are doing and how they are doing it. You have to practically participate, I think, in order to develop yourself.

If I'm serious, yes, I'd like to have done what Shakespeare did... to act and write. You learn so much from acting. One of our great writers, Alan Bennett, does both supremely well. When I write a story, I tend to speak it aloud as I'm writing it.

The idea of critical windows extends beyond just vision, of course: almost every system in the brain has a critical window when it needs to experience certain stimuli, or it won't get wired up properly. The most obvious example is language: if you don't learn a language early on, it's nigh impossible to become truly fluent.