I think the one you mentioned, "Losses are part of the game" is the most important. It builds character before anything else. Strategy is the easy part since it's all in the mind, you can research, copy others, or learn through experience. But if you're not disciplined enough to accept losses, then everything you've learned becomes useless, because you won’t be able to execute your game plan properly.
Losses are not the reason to give up, but instead it will motivate you to improve even better not just to overcome those losses, but should go beyond it. That’s where discipline should enter the picture. While it’s a smart move to gain skills and working strategies to maximize the potential outcomes, but for any trader or investor to remain in crypto, it takes a lot of discipline and courage to keep going and to move forward.