For me, mentally fit and emotionally fit, because even you have knowledge and skills these two kinds is essential in trading, especially in emotions. There will be a time that you will lose money because, in trading, unexpected always happens, especially here at cryptos. Also, you know that risk is very high if you invest a massive amount of money that you can't afford to lose so if that happens its much better to prepare your metal emotion.
For me, it is always the market cycle risk and the decisions that appear as a result of fluctuation in the market cyclical scenario. I have been in the market for more than four year and understand the market cycle pretty much. The risk associated to the market cycle that is FOMO and panic sell of your Bitcoin are some of the risks that often lead you to loss of value.