Note the emphasis on qualified. This philosophy plays to every employees strengths, and compensates for their weaknesses. It gives them the ability to grow, while allowing you to gain a comfort level that you have made the right selection. Monitoring this process is a very intregal and critical part of it. Learn from your experiences and do not repeat them.
Nobody picks up immediately, at goes right to the highest level of experience.
It takes time, nurturing, a well planned training program, successes and failures, and lots of patience. Without patience, this will surly fail. Often, you did what you could, both sides tried, but the experiment fails for a variety of reasons. The person had a chance, may have another one in the future, but for now, goes back to being a valued production worker, as they must have been before you selected them for training. They need to know, and to have seen in happen with others, that only a percentage of people put into this program will move up to the next level.