I think overconfidence is a big thing as well. There's a concept called the newbie luck. Say you're just starting and you don't know much of anything, you run your book in the first month and you catch a few lucky breaks, it goes well and you're up like 10% overall. You start thinking you are the man. You think you have the right instincts based on predefined biases and things you think you know. But frankly, you don't even know what you are doing. It is called unconscious incompetence. It means you don't even really know what you don't know. But you start believing you can do this. And it ends in a bad way. In the red zone.
You know, you should always have confidence in yourself but you also stay humble and flexible too. You need to have a humble mindset.
Indeed, overconfidence is quite hard to notice in time and react appropriately especially if you underestimate how hard for a retail trader to find an edge that can beat market consistently. Then lucky streak of trades can prompt you to increase your risk exposure, this is where the market can give you a painful and expensive lesson.