Arnold Jacobs:

The most common problems
Although many students come to Jacobs complaining about embouchure problems, he rarely finds problems with the embouchure.
"The most common problems I have seen over the last sixty-odd years I have been teaching are with respiration and the tongue. Surprisingly enough, I rarely find problems with the embouchure. That might sound strange because people come to see me because of problems with their embouchure, but frequently it is the embouchure reacting to a bad set of circumstances and failing it is simply cause and effect. If we change the cause of the factor, it is easy to clear up the embouchure. The embouchure is not breaking down, it is trying to work under impossible conditions.
When you are starving the embouchure for air volume, giving it all sorts of air pressure but not quantity, it cannot work. Very quickly you will be struggling to produce your tone. Just increase your volume of air not by blowing hard, but by blowing a much thicker quality of air. Very frequently the air column is just too thin."

(page 218 - ARNOLD JACOBS: SONG AND WIND)

Used with permission from Brian Frederiksen.