The two forces
Fear and greed are the two emotions most responsible for trading losses. Greed pushes you to take too much risk, hold winners too long, and chase moves you missed. Fear pushes you to cut winners short, hesitate on good setups, and freeze or panic when a trade goes against you.
Both are entirely natural human responses to money at risk, which is exactly why they are so dangerous. You cannot switch them off, and pretending you are immune to them is itself a form of overconfidence.
How they sabotage decisions
Greed shows up as increasing size after a few wins, ignoring a plan because "this one is different", or refusing to take profit because more always seems possible. It tends to strike right after success, when confidence is highest and caution lowest — which is precisely when overconfidence is most expensive.
Fear shows up as closing a good trade the moment it shows a small profit, unable to bear the risk of giving it back, or as freezing while a loss grows because acting would make the loss real. Both emotions push you to do the opposite of what a calm plan would dictate, and both feel completely justified in the moment.
Why structure beats willpower
Leverage amplifies both emotions, because larger swings in money provoke stronger feelings. This is another reason to keep position sizes small: a trade that cannot hurt you much is far easier to manage calmly than one that threatens real damage.
You will not out-discipline fear and greed through willpower alone in the heat of the moment. What works is structure decided in advance — predefined entries, stops, targets, and position sizes — so that fewer decisions are made while emotions are running high. The goal is not to feel nothing, but to have already decided what to do before the feeling arrives.