It seems counter-intuitive to let employees make mistakes, but it really is the best way to teach and to help staffers become leaders themselves.
When I was learning to drive, the duty of teaching me fell to my dad because, I suppose, he had actually been through a World War and was less likely to crumble under the stress.
For some reason, during one lesson, my older brother tagged along. At one point my dad told me to stop, and by stop he meant press gradually on the brake until the vehicle came to a standstill. But of course, I instead pushed abruptly on the brake which nearly sent us all spiraling through the windshield. In fact, it did cause my brother to slide forward dramatically until his lower legs were temporarily wedged under the seat in front of him. As he yelped dramatically, my dad told him to be quiet and leave me alone.
There were a couple of dynamics going on here. First, my brother was obviously not seriously injured, and my dad was thinking that mangled shins was scant payback for all the little sister noogies my brother had inflicted on me over the years.
Second, my dad knew that if I got upset or nervous at such a pivotal point in the learning process I might lose what little confidence I had and never get my driver's license. I learned on that day how to brake properly but not because of all the exaggerated drama coming out of my brother but because my dad was calm and let me figure out what I did wrong on my own.
While I recognize that modern workplaces can be too hectic to take this kind of approach to employee training, I really think it is the best way to go. For an employee to truly develop professionally, she has to learn by her own mistakes. And a manager's hysterical reaction to those mistakes isn't going to do any good. All that does is make an employee avoid repeating a mistake because she wants to avoid her manager's wrath. Isn't it better for an employee to understand a mistake in terms of procedural problems it caused? Through mistakes people learn the answer to the questions "why?" and "why not?" If the answers to those questions are more meaningful than "because your manager wants it that way," then the learning is internalized and sticks better.
Of course, you can't afford to let employees make costly mistakes as part of the training process, but if you micromanage them every step of the way they won't have the knowledge or the confidence to form opinions on their own or the confidence to carry through on them.