Back in November, I wrote a long essay about two years of splitting my time between Mexico City, London, and Hong Kong. Some of it was practical logistics such as tax residency and health insurance, but a big chunk was about the social differences between the three cities. The questions people ask when they first meet you. How far in advance you need to book a dinner. Whether you’re more likely to end up at a house party or a pub.A number of you commented on those social differences. Several people said they recognised their own city in the description. A few said it had made them see their own default assumptions about socialising differently. One or two said it had made them realise how much easier they’d had it somewhere else, and how much they’d taken that for granted.That essay only described part of the picture. A place and its culture are two of the four things that shape what it feels like to make friends. The other two are just as important, and …