For me, it was playing a musical instrument (transverse flute, then shakuhachi) that showed me that I really don't know how to breathe deeply with my diaphragm. Or, that I wasn't aware of it at all, now my breathing is more conscious, and I tend to focus on it many times, for example, when I'm just walking on the street. Concentrating on your breath is a great way to stay rooted in the present and become aware of your thought processes. Breathing is magical :)