Nobody has the whole picture. I would say that the more extreme an individual event is, the easier it tends to be to understand in retrospect. This depends greatly upon one's analytical sophistication, level of market data, fundamental product understanding, and professional network (to know what happened in other firms).
It's enormously cheaper to do business on markets nowadays. Back in the old days, spreads were sometimes multiple dollars on human-made markets with a lot of inventory.
With HFT, people compete to offer the best market, and spreads are in the pennies.
