I think Lee knew a significant truth about the men in his army, just as I learned that truth 150 years during my own service with the army.
Soldiers know when they are being lied to.
It's not that they are any smarter than their leaders or regular folks, it's just when they are in the ranks being lectured to by their leaders, they know what's true and what isn't. Maybe it's a deeply buried survival instinct, maybe it's because military life strips one's self down to the bare animal instincts, but they know.
When I was a First Sergeant calling my company to attention in formation and watching them when a high-ranking officer from division would come down for an inspection and 'talk,' I could always tell the instant the soldiers would "turn him off" when he began trying to lie to them. It wasn't that they were bored and set their minds to wandering (although that did happen at other times), but there was almost a universal switch the soldiers would activate when the tall tales began or they knew they were "in for it" because this high hat needed them to do something very unpleasant.
I think Lee knew that he could not lie to his men, ask them to do things that would bring about horrible injury and even death, without telling them the truth. Part of that truth had to be in his actions too in the face or real danger. Yes, he probably knew he had to "put on a show" once in a while for them, but when the chips were done and it was all in, so was Lee and his men knew it.
In my 20 years of military service, I have known two officers I would have done anything for because of their courage, care and concern for their men and I and those men knew it. Lee was even more rare, in my opinion, knowing what it took to get those men to trust him with their lives.
He wouldn't lie to them.
Just some thoughts,
Unionblue