From Lights Out: Pride, Delusion, and the Fall of General Electric (2020,)

Buybacks are controversial. Some see in them a lack of good ideas from management. Others see them as a kind of second dividend, a way to “return cash to shareholders.” The approach to deciding whether to buy back stock advised by Warren Buffett and his longtime business partner Charlie Munger has two simple prongs: a company must have plenty of capital to run its operations, and the shares it repurchases must be selling “at a material discount to the company’s intrinsic business value, conservatively calculated.”