The Japanese character for peace is literally "quiet mind".
My mind, however, definitely tends toward the active. I will wake up at 3am, and my brain will start downloading everything I have to do. I am usually engaged in at least two different chains of thought, and reading several books at once. I’m not ADD, but my mental RPMs are always high.
That’s why Isaiah 26:3 is hard for me… "You keep him in perfect peace whose mind is stayed on you,
because he trusts in you."
The word "stay" there is the hebrew word camak – to rest upon, to bear the weigh of. The art of a quiet mind is being able to quiet my mind upon command. What a great lifeskill (that I am still struggling with). I can only quiet my mind when I fully trust God to "bear the weight" of my life.