Having a mechanic who understands how things work and being able to explain to a customer in an understanding way are invaluable. Do you know what a differential is for and how it operates? What about an alternator, piston, u joint? Do you know what they are for and their functions?
Many of the cars today rely on electronics and often times troubleshooting means hooking up to a machine to diagnose. However, understanding how a car works and the issues its having, a good mechanic can sometimes use their sense of hearing and seeing how the vehicle is performing to diagnose the problem.
There are numerous vehicles on the road today, each with their own nuisances. Learn all you can about them. Try working on older vehicles to broaden your knowledge and appreciate how they were constructed.
Having a good working knowledge of how things work can be transferred in other ways such as building projects, troubleshooting, care and maintenance. Continue to expand your learning, share your knowledge and become an expert in your field.