Patience is a key, I see alot of "techs" who freak out when things don't go right. They lose it and there goes any chance of figuring out the problem. If someone really understands the theory( and by that I mean as applied in the real world), they should be able to troubleshoot. Whether they are good at it depends on their ability to work under pressure, with people looking over their shoulders and the amount of patience they have.
