Since the market is made by each of the participating banks providing offers and bids for a particular currency, the market pricing mechanism is based on supply and demand. Because there are such large trade flows within the system, it is difficult for rogue traders to influence the price of a currency. This system helps create transparency in the market for investors with access to interbank dealing.
The problem is that this is where traders are most likely to succumb to overconfidence bias. It's not uncommon for traders to complete a winning streak and then believe that they can't get anything wrong in the future. To believe this is of course unwise, and is only going to end in failure. Make sure you always analyse your trading sessions and look at your wins and losses in detail.