For every yin there must be a yang. For every positive action there must be an equal and opposite reaction. This is the way nature works. This is the way the universe works. And here's an important factor to note; We (our bodies) are designed as a part of nature, as a part of the universe. Our body functions on the basis of balance (homeostasis).
I've been caught up in certain things, at certain times over the years, just as we all do at some point. We lean more in one direction. We focus more on one element for too long, and eventually we become out of balance.
Society today typically focuses on one element at a time. We see/read about the "perfect" workout, the "perfect" way to eat etc... We all need the reminder that there is no such thing as perfect. There is also no such thing as "that one thing" or "that one way". In addition, we need to be reminded that creating habits as a whole, in a balanced way, will produce the best and long lasting results.
Make sure for every Yin you do, there is a Yang....