When you can simply 'do' tai chi, you are a skilled exponent. You have transcended the point where conscious thought intrudes.
At this point in your learning, you can perform tai chi very well but could not realistically teach what you can do.
To teach, you have to methodically unravel the process that got you there.
When you can dismantle how you got there and teach it to others such that they can do it too, you are an instructor.