Here's why I might not notice if you changed your hair or got a new outfit or you're now limping on the other foot.
When I look at you I see everyone you've ever been to me. If I knew you as a child, I see that child, and the teenager and young adult and old friend, all the people you've been at every age in every stage of our relationship.
No, that's not quite right either, because I don't see the physical details, but rather the inner person, the light in your eyes when you're telling me about your day, the blush in your cheek when you're embarrassed or flustered, the way you shake your head as if you can't quite believe my latest folly. If we know each other that well, I don't have to look at you to see you, because your image is etched on the back of my eyelids, and our story is carved into my heart.
So if I don't pick up on the new hat or the new attitude, it's not because I don't care. It's because who you are to me is so much bigger than the two of us in this place at this moment. We are our history, and the here and now is a chapter. We encompass each other, and that can overwhelm the new boots, maybe even the new horse.