in my opinion being greedy is the biggest problem that begineers do, we don`t know when to quit and always become positive regarding prices, but in reality they are not as good as we see but we keep holding and not cutting the loses.
Greed is really the main problem. Not selling because "it can grow even more"? Check. Going all-in? Check. Staying in dying currency because hodl is the key? Check. Trying to trade on unstable market which can go up or down? Check.
Greed is trader's worst enemy.