When you are accomplished with adjustment, a very small movement can be used to immediately affect the attacker's centre.
This imperceptible touch instantly renders the attacker subtly off-balance.
As the attacker seeks to re-gain the advantage, the student must continue to adjust themselves in order to maintain the uproot.
Presence, sensitivity and a lack of self-consciousness are all required.
The subtle adjustments taught throughout the Yang Cheng Fu form now come into play.
Overt, unnecessary stepping would break the connection between attacker and defender, rendering the tai chi ineffective.