Yea, I think it’s because when we plan out what to say, it gives our brain a goal and thus a framework for our brain to consider what we’re saying as an error, which then creates a block. It’s like that experiment when a group of kids were asked to build a tower out of uncooked spaghetti noodles, and a group of college graduates. But the small children built taller towers, partially because the college graduates had too many rules in their head, which blocked creativity. While the children were free in the mind and had no framework to block their creativity.