It's not about displaying empathy, it's about addressing what will actually help the person, and complaining almost certainly won't.
The quote continues: "Well, you can say that’s waggery, but I suggest that every time you find you’re drifting into self-pity—I don’t care what the cause, your child could be dying of cancer, self-pity is not going to improve the situation—just give yourself one of those cards. It’s a ridiculous way to behave and when you avoid it you get a great advantage over everybody else, almost everybody else, because self-pity is a standard condition and yet you can train yourself out of it."
The quote continues: "Well, you can say that’s waggery, but I suggest that every time you find you’re drifting into self-pity—I don’t care what the cause, your child could be dying of cancer, self-pity is not going to improve the situation—just give yourself one of those cards. It’s a ridiculous way to behave and when you avoid it you get a great advantage over everybody else, almost everybody else, because self-pity is a standard condition and yet you can train yourself out of it."