I don't agree with your premise that procrastination is based only on doubt or fear. I certainly didn't put off ironing my clothes for 3 days because I was nervous about my ironing performance. I think it's a combination of expected pain of the actual task (ironing sucks), ambiguity on the scope of the task, and potentially fear of how your output is perceived.

That's why many times, the best suggested procrastination treatments for a task are just starting the task (where predicted pain of the task disappears and you get clarity on next steps) or breaking down the subtask into very small subtasks that are digestible.