Much has been written about Société Générale's maverick trader Jerome Kerviel who, despite costing the bank $7.2 million, still hasn't been fired, reports The Wall Street Journal.

Trouble is sooner or later, these traders do get caught out. So what motivates them? What drives them to act as if they are omnipotent and can get away with anything?

One of the best explanations I have seen comes from Bloomberg's Michael Lewis.

"The story of Jerome Kerviel is less a tale of an evil genius at work than of a dull young man being acted upon by events almost beyond his control. I may be wrong about this, but so long as everyone else is guessing I might as well, too. And here's my guess: Jerome Kerviel never imagined himself in anything like these circumstances. They just sort of happened to him in stages. Stage 1 would have been his initial decision to be more like what he imagined a real trader to be than what he actually was - a functionary on a trading desk. His job was to arbitrage price differences between identical stock-market indexes. In doing this he naturally developed a view of the stock market, just like a real trader. His view was that it was going up. Thus, one day, filled with conviction, instead of buying one market and selling another, he buys one market - and then neglects to sell the other. It's such a small act of rebellion that he barely bothers to hide what he's done. One of the striking things about rogue traders is that they always lose money. Perhaps they just are born with an incredible knack for being wrong about future market direction. Or perhaps, if they guess right, they aren't exposed by their employers as rogues....As I imagine it, young Jerome pretty quickly finds himself staring at a shocking loss. Thus he enters Stage 2: doubling up and averaging down. The market is falling but he's buying it ever more cheaply and if he just keeps doing it the market will eventually rally, and he'll make it all back. Now all of his day is spent frantically making bets and hiding them. 'If it rallies and I get back to even no one will ever know,' he thinks to himself. If he wasn't a 'quiet loner' before, he is one now ... He walks home one night and there is something about the durability and grandeur of Paris. It gets him thinking. He is long $60 BILLION in equities. That's more than the market value of the entire freaking bank. And no one knows! Maybe no one will ever know! Maybe he can just keep losing billions, in private."

As Lewis explains, these accidental rogues are caught in the grip of forces that were simply beyond them. In one sense, they should be pitied. But then you remember that ordinary people, investors, have been screwed in the process and have lost money.