Holding the door won’t change the world. It might change the worst morning of the person walking through it.

Small courtesies are usually dismissed because they are measured against the wrong thing. Nothing structural shifts when you hold a door, which is true and beside the point; what shifts is one person’s experience of one difficult morning, and you have no way of knowing whose morning that is. The scale is tiny and the timing can be exact.

Do the small decent thing without evaluating whether it matters. Let the car in, carry the bag, say good morning properly. Impact you cannot measure is still impact, and it lands on people who never tell you.