Here is the quoted text on this feat;
Steady Engagement (Combat)
You can draw on your excellent balance to trip or disarm opponents when they try to disengage.
Prerequisites: Worshiper of Irori, Combat Reflexes, Stand Still.
Benefit: If you use the Stand Still feat to prevent an opponent from moving, you may make a disarm or trip combat maneuver against the target as an immediate action.
The question is, what does "use the Stand Still feat to prevent an opponent from moving" mean. Does it require SUCCESSFULLY using the feat, or just making the attempt?