Shohei Ohtani began playing baseball in the second grade of elementary school,
after joining the Mizusawa Little League in Iwate, where his father — a former company baseball player — was closely involved.

Although Ohtani was relatively tall for his age, he was still physically slender and far from a finished product.
Even so, his athletic ability stood out, and he showed exceptional promise both as a hitter and a pitcher.

Despite that talent, Ohtani was unable to reach his goal of competing in a national tournament during his early years.
No matter how hard he tried, the team could not break through.

That changed in his final year of Little League eligibility, when he was in his first year of middle school.
That season, the Mizusawa Little League went undefeated within Iwate, advanced through the Tohoku tournament, and earned a spot in the national competition.

In the Tohoku semifinal, Ohtani delivered a remarkable performance, striking out 17 of the 18 outs in a six-inning game.

Looking back, Ohtani says that performance was made possible by all the frustration he had experienced before.
Those losses taught him something essential —
without disappointment, it is impossible to truly develop the determination to win.

The final year was filled with relentless effort.
The frustration of losing, and the joy of finally winning, remain vivid memories for Ohtani even today.

Source

This quote comes from a Japanese book published in Japan and is not currently available in English.

Shohei Ohtani: Baseball Soaring Years I – Japan 2013–2018, p.63