A book I read explains blocking in great detail and is the only explanation that I have ever felt relevant (after 30 years of stuttering). It is a learned defense behavior against stuttering repeats- like the original commenter said. The book I read was great, although super wordy (oh, the irony), is “How to Stop Stuttering & Love Speaking: EXPANDS ALL EDITIONS of Stuttering & Anxiety Self-Cures”. It has tactics to help get around blocks and form positive habits.