You've lost ground on an issue very important to you. A ton of ground, perhaps in one fell swoop. So much ground that you either can't stand your homeland anymore, or fear for your safety if you remain. Or perhaps you've simply slipped through your current society's cracks, and can no longer properly function within it And you don't feel very much if any hope of things going back to an acceptable state anytime soon.
However, there's somewhere else that remains acceptable, and is in fact more acceptable than where you are now.
If you have the means, what do you do? You vote with your feet. You go to the greener pasture and you don't come back.
As previously mentioned here, this is currently happening in Arizona as Hispanics of all stripes flee the state in response to their new immigration law. You'll also hear threats to invoke this in the runup to any Presidential election- 'if X wins, I'm moving to Canada'. (Only a handful actually do it.)
The term is sometimes used for things as mundane as quitting a job, but that's not really what we're talking about here.
Officially, it's known as the 'Tiebout model', after Charles Tiebout, who put forward the theory in 1956, in response to the 'free rider' problem: that there are those in society that consume more resources than their fair share, and/or contribute less. He assumed that, assuming perfect conditions and perfect information, people will move to the place most suitable to them. Specifically, assuming these conditions:
1.Mobile Consumers: Consumers are free to choose where they live. There are no costs associated with moving.
3.Many Communities to chose from
4.Commuting is not an issue
5.Public Goods do not spill over of benefits/costs from one community to the next
6.An optimal city size exists: Economies of scale
7.Communities try to achieve "optimal size"
8.Communities are rational and try to keep the public 'bad' consumers away.
Of course, most of these are unlikely to occur in any given case, and for them to all happen at the same time is unheard-of. Perhaps if people could pick their time to move, but if you're moving in response to some external force, you're rarely ready for it. More often it's going to be something of a rush job to the first place that looks halfway decent; maybe just simply wherever there's a pre-existing family member.
And in a sudden exodus, assumptions 6-8 are going to be thrown out the window. Someone is probably getting flooded with a whole lot of people in a short amount of time.
What happens to the place left behind? Nothing good. When people vote with their feet, they're taking all their stuff with them to the new place. Money, possessions, a teeny bit of the existing or potential labor force. Every time someone goes, that's a little prick on the finger of the old location's general economy. Enough people leave, and it can cripple the old location with ease, as we're currently seeing in Arizona. In addition, there's a brain-drain effect- the smart people, the technically-skilled people leave, even if it's only a side effect of everyone else leaving too. Remember, everyone voting with their feet is in agreement with each other that whatever just happened, they don't like it. That's a lot of people that, until that point, may have been able to reverse the course of the new policy. The more leave, the more the old location is locked into the new policy, as there is less remaining opposition to it. Whatever they just did, they're going to end up seeing it, and all the consequences both good and bad, intended and unintended, through. They will be rendered, to put it bluntly, simply too stupid to fix any problem they've created.
Or put in Simpsons terms:
While Arizona is seeing a sudden effect, a longer, slower burn has been seen for years, decades, from Rust Belt to Sun Belt, as a decaying regional economy has sent and continues to send northeasterners and midwesterners south and west. Both, however, suffer the same effect: an economy lagging behind their peers. In the grand scheme of things, both pale in comparison to every mass exodus ever brought on by violence of all stripes. In the end, though, all wind up sharing a miserable aftermath.
After all, whatever problem you as a government were trying to solve in the first place will soon be the least of your worries if you suddenly have nobody left to govern.