Instability Rising: Why 2020 Will Be Different

Economically, the 11 years since the Global Financial Crisis of 2008-09 have been one relatively coherent era of modest growth, rising wealth/income inequality and coordinated central bank stimulus every time a crisis threatened to disrupt the domestic or global economy.
This era will draw to a close in 2020 and a new era of destabilization and uncertainty begins.
Why will all the policies that have worked so well for 11 years stop working in 2020?