Just thinking about thinking

The first time I met Jonny Rasmussen was in college. Although Jonny's an American, he spent a very large portion of his life in Japan, from elementary school all the way through high school. Thus, he's fluent in both English and Japanese. (People who spoke to him by phone in Japanese would often assume he was a native speaker, which would lead to some surprised reactions when he told them his name.)

Once, at lunch, one of us (it might have been me) asked him what at the time seemed to be a perfectly reasonable question. "What language do you think in?"

Now, having spent a decent chunk of time living in a foreign country and doing my best to learn the language, I realize how silly a question that is. One does not consciously choose to think in one language or another; it just happens.

I wonder why it took so long for me to figure that out?