Doomsday by Warwick Deeping

Meanwhile, Clare Biddulph kept three cool fingers on the pulse of her sister's marriage. That the marriage was not an emotional success seemed to her fairly obvious. Mary was a warm-hearted creature, and not a little impulsive, but too warm a heart may prove disastrous. Moreover it is not wise to deliver homilies to a young woman who happens to be very much in love with herself, and very full of her house and her wardrobe and her jewellery and her car. Mary had a very pretty swollen head; she was Mrs. Fream of Hill House; her smartness was growing.

Clare touched the relationship coolly. There were certain things that she wished to say to Mary, but she doubted the ripeness of the soil. Platitudes are truths that are always being rediscovered, but there are certain platitudes with which a married woman of experience is familiar, but which cannot be breathed over to dear friends. A woman may write of such things in her diary, but she will keep that diary under lock and key.