social skills
Letters to dear Julie are more interesting as the book, La Nouvelle Heloise, progresses to Part II. It becomes more interesting once the two lovers separate and start adding glimpse of observations about their surroundings, rather than rambling on about their mutual affections and torments.
Saint-Preux remarks in one of his epistles, "How can one be the friend so quickly of someone he has never seen before? The honest concern for humanity, the simple and touching outpouring of a sincere heart has a language quite different from the false demonstrations of politeness and the misleading appearances that the custom of society demands. I am greatly afraid that the man who treats me at first sight like a friend of twenty years standing might treat me at the end of twenty years like a stranger, if I had some important service to ask of him; and when I see such profligate men take so tender an interest in so many people, I readily presume that they are really taking one in nobody".
We find many of those nowadays--they are the essence of the human network. Sincerity alone cannot help you make your way in society; it's fully appropriate to follow customs and demonstrations.