It was a far cry from just two years ago, when Young was the up-and-coming N.B.A. darling who unexpectedly led the Hawks to the Eastern Conference finals after the team had missed the postseason three years in a row. This time, Young gave the Celtics fits — averaging 29.2 points and 10.2 assists over the series — but Boston dumped Young’s Hawks from the playoffs in six games. Now Young, who just finished his fifth season, is facing an existential challenge more daunting than any one playoff round: the Narrative. And how is he continuously taking his game 1 percent better, 2 percent better over time?

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