It's easy for traders to feel confident in their ability to remain calm and collected during their trading sessions before the market opens. However, once the clock starts it's a different story. When faced with real financial decisions, it's very easy for emotions to come into play. We can't avoid our emotions, but we can learn to work around them.
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.