If it's any comfort at all, the rules which apply to actors don't apply to stage managers, technicians, designers or arts administrators. We're allowed to screw up: in fact, when we do screw up, it's usually the actors who have to wear the damage.
I'd be curious where people think directors fall on the 'second chances scale.'
As a student, I have to say I wish these issues of how to succeed are crucial, and the prevalence of low pay/no pay internships creates a tight spot for those who need to make money over the summers. Last summer I was lucky enough to be able to take an (unpaid) internship with a great local company, which gave me my first professional credit because my grandmother offered to pay for my housing since I was taking some classes as well. A large number of my classmates were not able to find internships, or even try to look, as the cost was prohibitive. I agree that internships for class credit can be a great compromise as it creates another source of 'pay' for the experience.