I think there is a cultural component to it. In some cultures public display of emotions (either sad or joyful) is not only "normal" but kind of expected. "Weeping and wailing and mopping about" over a loss of a close family member are "mandatory" in some cultures. However, your advice, James, seems to be more about the ability to control the free flow of emotions at the personal, "private," level, regardless of cultural norms. People may chose to comply with societal rules in public but the point is not to fall into the "habit of grieving" in private, not to derail your life because of a tragedy, whatever it might be. This is such a stoic idea. Great advice.