For this post, by "dog handler" I just mean "anybody who handles a dog." Not necessarily a show ring handler, or a police dog handler. So...I mean *you!* As your dogs owner, you are most frequently its handler.
What makes some people seem to do really well with even the most challenging dogs, and some people flail with calm and well-trained dogs? The answer is in your handling skills. Note that I did not say "the answer is in a magical way with animals that some people have and some people do not have." Like any skill, most people are not born with it, but it can be learned!
So, what goes in to being a good dog handler?
1) When handling a dog, you set the dog up to succeed rather than fail. Taking a young, semi-trained dog to a busy location like Portland Saturday Market is usually a recipe for disaster. A more experienced handler would have known that their dog is in no way prepared for that level of excitement and distraction, and likely would not have even brought the dog.
2) When handling a dog, you can predict what the dog is most likely to do at any given moment, and you can ready yourself for interruption, prevention or reward as needed. If I am walking Dog A down a squirrel-ridden trail and I know that Dog A has been doing distraction work for months and is very good at it then I will be expecting to dispense "Goood"'s and the occasional "Yes"/treat for a particularly challenging squirrel. If I'm walking Dog B down the same trail, and I know he is very distracted by squirrels then I will be ready to interrupt a chase attempt. If I am walking Dog C down yes that very same trail, and I don't know Dog C and have never walked him, then I will expect that he will not be good with squirrels (because most dogs aren't) and be ready for interruption, but equally ready to reinforce a correct response.
3) When handling a dog, you always keep in mind that your attention, interaction and access to resources are of prime value to your dog. You don't give this stuff away, and you certainly don't use it to reinforce incorrect behaviors. If I am going to take my dog to the off-leash section of the park, I'm going to frame it to the dog as "You walk politely up to the off-leash section, and I will reward you by taking the leash off." What if my dog had pulled and drug me to the off-leash section, and then I went ahead and unleashed? I would have totally been rewarding that pulling and dragging behavior! Good handlers keep in mind that they have control of all this stuff, so dole it out for good behaviors.
4) Good handlers can tell when a dog truly, honestly can not do something versus the dog just doesn't feel like it/wants to do something else versus the dog is too distracted and/or doesn't know the command well enough. If you say "stay" and the dog doesn't stay, do you know why? It could be because the dog is afraid of something and can not sit because it is too fearful. Or it could be because he would rather stand or walk and sniff at things on the ground. Or it could be because he's not practiced "sit" very much and never practiced outside and thinks that "sit" just means "sit in the living room." Whatever reason your dog is not performing, there is a specific protocol to follow -- for the fearful dog, your first job is to get the dog to not be afraid, so you'd stop with obedience for now and work to build up confidence. For the dog who doesn't feel like it, you would limit or restrict his access (probably by shortening the leash) and re-cue. For the dog who doesn't really know the command, you'd make a note to practice that one some more in an easier environment, then bring the dog back and try again.
5) Good handlers have good mechanical skills. I think it was the writer and trainer Jean Donaldson from the San Francisco Society for the Prevention of Cruelty to Animals who first noted this. There is a lot of timing, rewarding, leash handling, etc. Good handlers practice a lot and are very fluent at this.
Like I said earlier, handling isn't something that you're either born with or you'll never have. Some people are very talented right off the bat, but even if you're not, you can totally learn this! And then practice! Soon it will be just like riding a bicycle!