He was wrong on MSFT. But at the time there were maybe 100 companies like MSFT, for example Worldcom, Enron, PET.COM etc. So if you average over those 100 companies that he didn't understand and didn't invest in, maybe he was right not getting into unfamiliar waters. There were a lot of risks that he could not foresee - potential rise of a competing OS, the rise of mobile phones (which even BillG did not foresee), anti-monopoly lawsuits etc etc.