Schedules seem to make some Js feel more confident and competent like they have control, or at least, it makes them appear so. Conversely, scheduling can take confidence away from Ps because they equally do not feel competent, because they do not have control of the situation (but in a different way, like 'Oh my God, I have to stick to this so how can I be in control? What if I go wrong now?'
Speaking as a strong P, I am not confident, though I might appear so because once I have thought long about a subject, and once I have done good research, I can improvise quite well. I will not pretend to be learned in things I don't know a lot about, and hence only improvise on a subject I'm sure of, if I talk about it at all. I do however know some strong ExxPs who might come across as arrogant to you, because they will get involved in simply anything for 10mins and then bluff their way through later as some kind of expert, that's only a few though.