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.
This is specifically referring to crypto traders, they need to learn how to trade because trading is very risky, it is easy to lose all your funds if you are not patient to understand the market analysis. Loses are part of crypto trading, no matter your experience and professionalism it still happens but the more you understand trading the lesser loses you will get.
Bitcoin investment is different, if you are holding for a long term you will not loses because price will always reach ATH in the future and you will always be more profitable when it happens. Altcoins investment is risky, like trading you can lose your money very fast, there are a lot of scam projects in the crypto market. Invest what you can afford in Bitcoin but invest what you can afford to loose in altcoins and crypto trading.