How much debt is too much?

The China Evergrande story is hitting the news on a daily basis lately. A very large public company indebted to the tune of 300 Billion dollars is unable to repay its debt. When does debt get out of control? Even with interest rates that have been at historical lows, it is clear that pushing on a string may be inadequate at some stage. While a bail out seems ever more likely, the risk of private debt being monetized into government debt will ultimately impact the whole country. Will this story be the spark that derails sky high valuations of all asset classes worldwide remains to be seen. The risk will likely be contained but Too Big To Fail will slowly become Too Little to Fail to Nothing Can Fail.