>Well 10% is better than less or nothing, right? Shows his lack of confidence in it going up any further - or at least within a timeframe that there aren't better investments.
Pretty much any good book about investing (eg. The Four Pillars of Investing) teaches you that following your human emotions and irrationality in investing is the worst you can do, basically selling when everybody IS selling is the worst move (Warren Buffett: Be fearful when others are greedy, and greedy when others are fearful, https://www.investopedia.com/articles/investing/012116/warre...)
So I'm pretty surprised to see Masayoshi Son acting like a rookie investor, and following the crowd of uneducated investors buying during the mania and selling during the crash
It's the opposite of investing 101