Via Jeremy Grantham of GMO

The good old days of the domination of the first generation quant models, where you simply show up with three concepts –
value, momentum, and discipline – are over. But, even more critically and, perhaps like career and business risk, out at the limits of
arbitrage, is this need for judgmental overrides on rare macro events. Quants like to show off their discipline by marching off the cliff in rows (it is said, I hope apocryphally, that Shaka, the great Zulu Chief, marched an impi, or regiment, off a cliff to impress European observers and I hope it did). Well, in real life it would be nice to stop at the edge and say “I don’t like the look of this, perhaps my model missed something.” The extremely diffi cult objective is to maintain the advantages of quant discipline 95% or so of the time and hand over to a human being when you reach the edge of the cliff.