The reason for the gap between Lee Kang-in and Kubo

Lee Kang-in — if you ignore him, he just goes for a lethal tackle.
Kubo — even when facing all sorts of humiliation as an Asian on the field, he remains submissive.
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That is the difference.
Maybe it's because Lee Kang-in's father was in the airborne forces, but he has no fear and never backs down.