How do people decide to make major life changes?

We can go great stretches of time without any big changes occurring in our lives – sometimes big changes happen to us and we are forced to change, but this is not very interesting from the perspective of self-directed change – yet sometimes we make radical changes in our lives at short notice, why? What experiences and stimuli facilitate these short-gestation, root-and-branch course corrections?

My curiosity here stems from my spontaneous decision in 2017 to quit my job and fly to the other side of the world, where I have remained (though often on the move) for the last five years.