$SPDR S&P 500 ETF (SPY.US)$$Invesco QQQ Trust (QQQ.US)$ | JP...

$SPDR S&P 500 ETF(SPY.US)$ $Invesco QQQ Trust(QQQ.US)$ | JPMorgan says crowded stocks sow the risk of an 'out-of-the-blue' shock.
Dubravko Lakos-Bujas, JPMorgan's strategist, cautioned clients they could be “stuck on the wrong side” of the momentum trade when it eventually falters, advising to diversify holdings and implementing risk management.
He repeated concerns over market volatility, saying, "It just might come one day out of the blue. This has happened in the past, we've had flash crashes,"
"One big fund starts de-levering some positions, a second fund hears that and tries to re-position, the third fund basically gets caught off guard, and the next thing you know, we start having a bigger and bigger momentum unwind."