I got Jean Donaldson's book "Train Your Dog Like a Pro" recently. I love her books and writing style. :) The book is one I would highly recommend for anyone wanting to learn how to train their dog. The thing that struck a chord with me was in the introduction which is titled the same as this thread. "What makes a trainer?".
She videotaped two sets of people putting dogs thru their paces. One group of people were dog trainers and the others not. There were obviously technical skill differences between the two groups. She said what really stood out was the way the trainers never stopped training. The non trainers would do a few repetitions and then stop. The trainers were relentless (her word) and it didn't matter if it was a novice dog or a fully trained dog, the trainers trained. The non trainers had a lot of dead time between training exercises. I've seen this many times over the years.
She points out that a person can love dogs but loving the training of dogs is completely different. Trainers love the process but nontrainer types love the result of the process. She points out, as all good trainers do, that perseverance is required. To have a trained dog, you don't have to be a professional but you must train. :)