At the vet, my dog Bowie spotted another dog in a blue vest and got curious. Before I could react, the receptionist snapped, “Can’t you see the blue vest? Keep your dog back.” The room froze. Embarrassed, I tightened Bowie’s leash, unsure what I’d done wrong.

Later, I Googled it: blue vests usually mean service dogs—working animals trained to assist people with disabilities. A curious dog could distract them and put their handler at risk. I felt awful. The next day, I saw the same woman and her service dog outside the clinic. I apologized. “I didn’t know yesterday. But now I do. I’ve learned.” She smiled. “Most people wouldn’t say anything.” Her dog’s name was Mercy.