It has been known since the 1800s. Yet we allow government and corporations to promote the idea that there is a need for unemployment, that it - like poverty - is inevitable. Neither poverty nor unemployment is a natural phenomenon. They are created by policies and actions of those in power.
In the US we talk about nearing a 10% unemployment without talking about the people who have been hidden. In the 1980s President Reagan took out the "discouraged worker" (those who have given up looking for work) from the number of unemployed. Some estimates are that these workers are another 10%. So in reality close to 1 in 5 workers is unemployed.
That is why full employment policies are good for health. Full employment policies are good for families. And Full employment policies are good for the economy.
It is working people who drive the economy. They don't make enough to hoard money away like the rich, so their income goes into products and services that keep people working. That's a reality that our corporate news doesn't promote. Unemployment kills - literally.