SoftBank Founder and CEO Masayoshi Son said Monday he was "foolish" for his firm's multibillion investment in WeWork. His comment in an earnings presentation came as SoftBank gave WeWork a valuation of $2.9 billion as of March 31 based on a discounted cash flow method, down from $7.3 billion as of Dec. 31, following its failed IPO. SoftBank has reportedly invested $18.5 billion in the company, according to a comments leaked in October from WeWork's chairman. WeWork's private valuation was as high as $47 billion before its botched IPO last year.