There must surely be a different answer to that question for each individual, but in most cases it will be a mixture of positive “pulls”, negative “pushes” and some element of chance. In my own case I left the UK to teach English in Japan because I was finishing university, had no idea what to do, and it was the midst of the early 90s recession so jobs at home were scarce. With no particular knowledge of or interest in Japan, chance played its part in the form of a mature student friend who had himself taught in Japan and recommended it. After five years back in England I little thought that those two years in Japan were anything other than a youthful sojourn, but again chance played its part and I once more headed east to work for at most another two years on a secondment in Japan. Thirteen years later I have never moved back.
Others’ stories will differ in the detail, but in my experience most will share elements of this tale. Milligan, the fictional hero of my novel, is “pushed” by the prospect of an enforced betrothal and grabs at the sudden chance of a diplomatic posting at the ends of the earth. Given the current economic difficulties there are no doubt many young people now taking jobs outside their own country, and some proportion of those – unbeknownst even to them – may never go home again except to visit. As John Lennon said, “life is what happens when you’re busy making other plans”.