Masayoshi Son, long known as a free-spending benefactor who encouraged startup founders to pursue their dreams even if it meant losing billions of dollars, had a different message for entrepreneurs last month: Your dreams had better be profitable.

The chief executive officer of SoftBank Group Corp. told company leaders gathered at the five-star Langham resort in Pasadena, California, that they need to become profitable soon and stressed the importance of good governance, according to a person who attended the event.

Public investors aren't going to tolerate gimmicks, like super voting rights or complicated share structures, that privilege founders over other stakeholders, he said, adding they should get in shape years before they consider going public.