I googled the author and book. She had the resources to travel the world looking for herself. In context her advice (not just the quote above) seemed to me ... well, C.S. Lewis described it:
‘I beg your pardon, sir,’ said Vertue. ‘I had not seen it in that light. I will certainly act as your servant for a day or so if you wish it. I had not understood that it would be such a burden to you to cook for yourself. I don’t remember that you said anything about servants when you were outlining the good life last night.’
‘Why, sir, said Mr Sensible. ‘When I outline the principles of the steam engine I do not explicitly state that I expect fire to burn or the laws of gravity to operate. There are certain things that one always takes for granted. When I speak of the art of life I presuppose the ordinary conditions of life which that art utilises.’
‘Such as wealth,’ said Vertue.
‘A competence, a competence,’ said Mr Sensible.
‘And health, too?’ said Vertue.
‘Moderate health,’ said Mr Sensible.
‘Your art, then,’ said Vertue, ‘seems to teach men that the best way of being happy is to enjoy unbroken good fortune in every respect. They would not all find the advice helpful.’