So the most fatal mistake in my opinion is following other people without having your own strategy and without your own research. In the past, I often saw friends FOMO into futures, in the end they lost. Even though trading on the spot is confusing, let alone using leverage. Now I prefer coins with good fundamentals and just HODL, it's safer.
I think spot trading is not that confusing, it's the safest to start as a beginner to avoid many mistakes because the loss on spot is quite accommodating, at least in spot, you loss only the value of your assets not your entire tokens at once unlike future. You only tell the beginners to run a thorough research to keep them vigilant and love the space more since that's the sacrifice a beginner can give not money.