Trader, using error account, trade using company money aka other people money, where his account is too big to fail then company continue to fund his account.
At first, no body found out, as he is the chief trader and also the settler which normally handle by two person. With this, he could cover all the traded which amount with huge losses with ease.
One fine day, positions get affected with one big bad news, where they have no way back but to continue to support the market.
His positions get bigger and bigger, with the exposure, the looses get so big that, Barring can no longer provide the funding to support the margin.
And soon, Barrings have found out the fraud trade, and the amount of lose have make the bank run out of liquidity. And soon the bank has declared insolvent, and NICK has been caught.
Lesson:
1. Trade with your own means.
2. Admit mistake, when it is a mistake.
3. Be calm and be strong