He is the fabled icon of Wall Street. He’s hyper-confident, decisive, unemotional, and prone to bouts of egotism. He (and more often than not it is a he) is a trader.
Traders sit at the coalface of the markets, glued to their screens, executing orders either on an agency basis or through the use of the firm's risk capital. For these beasts, P&L is the only thing that matters.