Trading is too complex an activity, because there is no one clear algorithm that would act the same way for everything. Therefore, every trader tries to create their own strategy that will work for them.
Most of them experience losses in trading because many people think trading is easy and even underestimate their knowledge about trading or even think they have mastered everything about trading properly. Even though it is true as you said, trading is something very complicated and all strategies cannot be applied to everyone because it all depends on our suitability for the strategy. Maybe lastly, every time you trade, keep learning, even pro traders never stop learning about trading and use failure in trading as an experience so you don't repeat the same mistakes.
Don’t be greedy, it sounds too abstract, and will also depend on the trader’s strategy. And traders lose more than they earn for the reason that they do not follow basic rules, do not share the risks in trading, and even perhaps simply choose not the most reliable coins for trading.
Greed is the root of all failure in trading, no matter how good the trader strategy we use, if there is greed then our trading will not be successful, greed is also related to emotions.