When you are at your job you dont wanna see as weird or awkward so you stutter. Is a defensive mechanism to prevent yourself from living your worst fear; being strange, unaccepted, different, unloved. It´s like people who have fear of failing and they voluntary sabotage they performance to fail or dont even try. If you dont try, you cant fail. It is in deed a strange phenomena because stuttering itself make´s you look weird so it doesn´t solve the problem. But your mind creates the blocking just trying to protect you from "harm". The mind can´t measure the social effect.