The highest yoga is the control of the mind, yet most of us have no comprehension how or why our minds work the way do.  One of the reasons is that we have not been taught about thought, what it is, where it comes, and how it affects our lives.  Those who are concerned about the health of their physical body are careful about the kind of junk food they eat but I'd venture to say they never think about the junk thoughts they carry in their minds....or how those junk thoughts affect the effectiveness of their being. Enough said at the moment.  Something to think about...how can you find out what kind of thoughts crowd your mind?  And how much of it is junk?