In the critical aspect of the writing process, the writer reviews, revises, edits, corrects, and otherwise polishes the writing. Unfortunately, most people are more familiar with the critical aspect of writing than they are with the productive aspect. If you believe that all writing uses your critical facilities, you may find it hard to produce ideas. Usually, when people say they don't like to write, they mean they don't like being critical of their own writing and don't feel comfortable revising or editing.
In the productive aspect of the writing process, the writer uses whatever discovery techniques work best. The critical attitude the "inner editor" is set aside while the writer writes freely.
The critical and the productive aspects are both necessary to the writing process. While, they may overlap or alternate rapidly, you will find it helpful to learn to separate them in your thinking and in your practice.