Ok this one takes a bit of explanation!
Basically to make a change in your life you have to actually embed it. First Act on it. then do it enough until its a habit and then it will be actually a change.
So in the context of yoga.... to get the benefits of a yoga. For it to make a lasting change in your mood you need to start doing it. Often. This is what the challenge is all about actually, trying to establish a yoga habit and then a yoga change in your life!
You know the feeling when you leave a yoga class. You're calm, you're centred. You're happy you gave yourself some time and you're ready to give your best self out to the world! Well you can get that feeling all the time! really!