Fmrstrtrcr nailed it. Education, education, education... Business classes, math classes, ELECTRONICS classes... I am absolutley amazed at how many young bucks "think" they already know what they need to know to repair cars, without ever having set foot in a classroom beyond high school. If you're going to the business, you MUST be able to diagnose and repair modern cars. BTW, if I were a youngster, I would be studying electronics and how they "work" in cars. THAT'S where the money is today.
Agreed, COMPLETELY. Get a job actually DOING it, so you find out early whether or not it's "for you". Use that job to 'work" your way through school. You may find other more lucrative avenues, and "use" automotive expertise as a "hobby".
When you understand the concepts behind what makes a car "work", it's much easier to diagnose and repair. A 20-year old was in my shop a couple weekls ago, bragging about his mechical knowledge, and how he could go to work in a dealership... Right... I asked him "How does a knock sensor work"? "Oh, that's easy. It tells the computer to change "things" when it senses knocking..." My reply "No, not WHAT does it do. HOW does it do it?" Deer in the headlites... Same question regarding air flow measurement. "Ohmes!" Duh... But HOW? Deer in the headlites. And these are two small examples. Explain what headers "do" (why they "make power"). Which is capable of more sheer horsepower: Carb, EFI or mechanical injection? (when gasoline is the fuel) Which is most efficient?
These are just a few examples of what a true automotive tech needs to know these days. The days of "tuning" the 327 under the willow tree are LONG behind us...