Can there be one magic skill?

In my previous posts (1, 2, 3, 4) I claimed that there is one "magic" skill that can be learned and having it or not more or less means being successful or loser. Several commenters pointed out that it's a black and white thinking, therefore surely wrong. They also noticed that I blame one skill for success/failure which is obviously nonsense. I'd like to explain how can it be black&white and only, despite both are not true.To talk about a "skill", it must have meaningful variance, ...

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