It works like this: Politicians find it in their self-interest to take from Peter and give to Paul, whenever Paul can offer more political support than Peter – in the form of votes, campaign contributions, get-out-the-vote efforts, etc. But as tax rates rise to pay for these political acts of theft, some of the Peters begin to emigrate to other jurisdictions. As more taxpayers leave, the tax rates needed begin to rise – leading to a greater exodus. Eventually there are no Peters left to tax to pay for all the benefits the Pauls were expecting.
In the United States I associate this general approach to politics with Franklin Roosevelt, who had two important insights.