>A similar thing happened with Bear Stearns. It beat the market consistently every month... until it didn't. IIRC it blew up very very quickly

Very subtle difference,though. I am simplifying things here but IIRC, Bear Stearns blew up because they wrote insurance for things they didn't think would ever happen (housing mkt going down) and had a lot of exposure vis-a-vis how much premium they collected (i.e. sold a put -- limited upside , unlimited downside). I doubt ARKK has _written_ put options. It might be the case that the value of the ETF will go down drastically but they won't go bust because of liabilities.