Classical Tai Chi is implicit "Mindfulness" of the direction

from Instagram

First concern is which direction

                 (video link)

It is pretty easy for most people to watch a movie and be "mindful" not being distracted at all...it is pretty stimulating.   For most beginners in Tai Chi however there is little stimulation, one might say mind/body sensation to be had when learning "does this arm go here, does that leg go there" etc. So one might say Mindfulness in Tai Chi at least for beginners is upstaging distraction with even lower stimulation, not higher...this is quite a task. Classical Tai Chi takes a different tact, it gets you going in the right direction first thing. Of course, this does take practice at home after class unlike the many forms of exercise where one can go to class then come home to days of no exercise.  Classical Tai Chi is also not a panacea for not being mindful, it requires daily maintenance.   So for most beginners in Tai Chi mindfulness is a practice for training your mind to focus more on what stimulates less and then move on to learning hand position, timing then internal discipline.  Notice I used the keyword "focus".  

Lots of Tai Chi instruction coupled with "mindfulness" asks that you be "aware", "be present", " know what all of your body is doing, etc. but this is all pretty difficult for beginners. Classical Tai Chi, on the other hand, assumes if you don't know which direction to be aware or present in it matters little how you are moving the arms and legs.  If you are lost in a giant forest and do not know which way to walk you could probably wave the arms for a long time and literally not get anywhere. Waving arms with no "internal movement" from the core is called "external" Tai Chi. 

In Classical Tai Chi  the ultimate goal is to learn "internal discipline" and every move inward directs every move outward.  Arm and leg movement without an inward movement is called "external" Tai Chi not "internal".  First things first however, moving in the right direction,not only teaches direction but also teaches the "internal discipline" of the lower body...how to move the legs from an internal movement of the core muscles.