My son does not look fragile, bending over a game or manhandling the dog. Certainly his body is strong and flexible, and is not easily harmed by me. I have bruised his body and then it has healed.
To a regular person, it is not apparent that another human being could be fragile like the old dictionary. Because of human's physical capabilities and emotional responses, other people tend to ignore the frailness of another human being (whether it's emotionally or physically).