So, gladly she did as she was bidden, but dipping him headfirst in the dark and bitter flood, she held on to him by one foot. Thus her fingers, pressed about his heel, kept the waters from reaching that one spot. By the time she understood what she had done it was too late, for the thing could not be done again; so ever after she was afraid for her son, always afraid.

—Black Ships Before Troy,
Rosemary Sutcliff

What element of a Greek myth does this passage contain?

the hero’s flaw
an explanation about the world
a god changing form
a moral lesson learned