Lethargy is moving too slow for the intended lead’s request (‘lead’ is the action, and not the person). What this really boils down to is the reaction time of the dancer that is a.) a lag from the time at which a request was sent to the time it was
There is usually a height difference between the partners, and usually, depending on which country you’re in that height difference is a Smaller Follower to a Taller Lead. See > Smaller Follower – Taller Lead.