>> One has to look out at the world and, taking in the successful and unsuccessful, conclude that some ego about oneself might be more or less required for success.
Well, if you don't think you pack a punch or can take a beating, you don't throw your hat into the ring.
The problem is always to know how to strike a balance- believe in yourself, know what you can achieve, but don't become an overblown bag of farts. Why? Because obviously nobody can stand knowing they're an overblown bag of farts, so if someone is, they don't know the first thing: who they are.
Socrates, the wisest of men, knew how to get out of this one. "I know one thing, and I know it well: I know nothing at all", he said [1]. And, he said, "know thyself" [2].
A scientist is driven by what she doesn't know, and wishes to know. But she must know the immensity of the task, lest she become an idiot who thinks she knows and knows nothing, John Snow.
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[1] my liberal translation of his laconic "εν οίδα οτι ουδέν οίδα", "I know one thing, that I know no thing".
[2] "Γνώθι σαυτόν".