Re: Who really does understand them?
Buffet called the dot.com bust in advance because he can count. So he looked at the balance sheet of a bunch of these companies and noticed that although they had rising turnover, and often were reporting profits (or predicting them for the future), they didn't seem to have the cash to match their claims.
He's also confident enough to publicly say, "I don't understand this, so I won't do it".
Before the great recession the head of one of the big European banks (UBS?) said something similar. That he didn't understand the CDO market - all those lovely mortgage backed securities that proved so disastrous, because they were impossible to value. So he stayed out of the market. In about 2005 he was sacked for not making enough profits. It's a shame we can't retrospectively go back and remove a bunch of peoples' bonuses from that era, and give some portion of them to people like him.