SoftBank founder Masayoshi Son loses $25 bn in tech's brutal winter

Masayoshi Son, SoftBank Group Corp.’s billionaire founder, checks the chart. Then again. Another time. And once more for good measure.

Lately it’s only moved in one direction: Up. 

It’s not a chart of the firm’s stock picks. Those are sinking fast. So too is Son’s fortune -- at $13.7 billion, it’s crashed $25 billion in the past year, according to the Bloomberg Billionaires Index.

The chart is SoftBank’s loan-to-value ratio, which Son says he checks four times a day. It’s key to how he staged his comeback over the past two decades after losing $70 billion during the dot-com crash.