As a professional dog trainer, I hear it all the time: "Why does my dog listen to you, but the minute I take the leash, it all falls apart?"

After decades of training service dogs, you'd think I'd have it all figured out by now. But recently, a five-month-old puppy reminded me of something fundamental.

We often assume that newer is automatically better. But when we look at dog training over the past 100-plus years, we see a mix of highs and lows.