Let's focus on the details of training design. In lots of training programs we tell people what they will learn, we set out a careful learning...

Let's focus on the details of training design.

In lots of training programs we tell people what they will learn, we set out a careful learning design, we allow for "safe" practice, etc.This generally alleviates concerns and allows the trainee to relax and take in information.  

That sounds good.  But we can design training to be more challenging and let learners experience failure.  Can allowing trainees to make errors in training be useful? Explain.