More than anything, trading emotions can hurt your account balance.
Or, as the famous trader Jack D. Schwager said in Market Wizards:
The key to trading success is emotional discipline. If intelligence were the key, a lot more people would be making money.
The wave of trading emotions
Emotions make us enter the markets at the wrong time. Exit at the wrong time. There’s the fear of missing out (FOMO). Emotions probably make us take wrong decisions in between as well. It is the reason we lose out, even when our trading strategy is solid. We are bound to make the wrong errors over and over again, unless we are aware of what’s working against us.