The key to playing in either the high or low register well is focusing on making music. As always, Mr. Jacobs seems to have found the perfect words to share with any student struggling with that.
I think it is safe to say that the instinct for most of us when playing in the extreme high or register is to want to use more power to "hit the notes." While using a lot of muscle (and for high notes, shoving the mouthpiece into our faces) helps us to "hit" high notes, it is always with a terrible sound that no one can blend with or tune to. It is also very likely that we will crack that note a high percentage of the time and get tired very quickly.
By telling the player to focus on playing melodically, we get the attention off of the physical aspects of playing in the extreme registers and towards simplifying things.
I am reminded of a great quote from Joe Alessi. He frequently says:
"Playing a brass instrument well is an incredibly simple process, and playing a brass instrument poorly is an incredibly complicated one."
Playing with power (using excess strength) is always a more complicated process that simply focusing on the buzz and thinking melodically.
And if it's good enough for Mr. Jacobs and Joe Alessi, it is good enough for me.