It's a specific sequence of dozens of poses, each different, each with countless aspects you learn and work on. There's so much going on, if you are actually trying to do it right, that there's no cycles left for your mind to wander.
Examples are the angle which you hold your arms and legs; the location of your center of gravity; keeping your knee behind your toes; direction of your gaze, engagement of stomach and perenium muscles; reaching as far as you can in extended poses; balance; remembering the name of the pose; synchronizing the breath with the movement; keeping the breath smooth and slow; learning your body's limits; working with pain; how to hold your hands; the list goes on. And it all works together in an integrated fashion to leave no stone unturned in your body.
Examples are the angle which you hold your arms and legs; the location of your center of gravity; keeping your knee behind your toes; direction of your gaze, engagement of stomach and perenium muscles; reaching as far as you can in extended poses; balance; remembering the name of the pose; synchronizing the breath with the movement; keeping the breath smooth and slow; learning your body's limits; working with pain; how to hold your hands; the list goes on. And it all works together in an integrated fashion to leave no stone unturned in your body.