I've read several explanations for his closed mouthed approach to planning. One, he believed his plans weren't open to discussion. Another that he feared tipping off Union forces (this in the case of his Valley campaign). From a psychological viewpoint, we can look at the example of leaders who tend to fly by the seat of their pants. Laying out a detailed plan ahead of time could thwart moves to take quick advantage of rapidly changing developments. etc.And as for Jackson as independent commander....who was his opposition? Jackson did well against the second string. And many of his peers and historians have faulted him for his refusal to keep subordinates informed of the overall plan. Lck of understanding of the commander's intent for a battle stifles initiative and flexibility. This caused some fo his issues at the Seven Days and Fredericksburg.