While Vegeta from the Dragon Ball franchise is one of the most fan-favorite characters to come from a Shonen series, he too had several regrettable moments. However, one can argue that those moments were the reason why he was able to shape himself into a warrior and character that fans know and love to this day.
One of his worst moments came in the Cell Saga when Vegeta was overconfident about his strength and allowed Imperfect Cell to find and absorb Android 18. Not only did Vegeta kick his son Trunks aside during this, but Cell also beat him up as he attained his Perfect form.
How did Vegeta's greatest flaw become essential to his growth in Dragon Ball?
As evident from the events during the Cell Saga, Vegeta made a huge mistake when he allowed Imperfect Cell to absorb Android 18. This essentially allowed Cell to attain his Perfect form, following which he was stronger than both Vegeta and Trunks.
The foolish part of this scenario was how both father and son were individually stronger than Imperfect Cell moments ago and could have finished him off. It was Vegeta's pride as a Saiyan that made him think that his evolved Super Saiyan form was enough to finish off Cell even if he were to ascend into his final form. Moments after Cell absorbed Android 18, he easily defeated Vegeta.
While fans were furious at Vegeta for the mistake he made, this behavior was very true to his personality as an individual and as a Saiyan. It has been seen several times in the series how overconfident Saiyans get when they have attained a new form.
Surprisingly, even Goku and Gohan displayed a similar flaw when they were fighting powerful foes. In Namek, when Goku was fighting Frieza, he asked the Evil Emperor to power up and fight with his full strength.
Fortunately, Frieza's full power did not surpass Goku's strength. Later, in the Cell Saga, Gohan could have defeated Cell soon after he turned into a Super Saiyan 2. However, his desire to make Cell suffer led to Goku's death moments later.
So, Vegeta's behavior during the Cell Saga was very true to his nature. As fans would know, Vegeta was a prideful character from the start, i.e., during the Saiyan Saga itself. Thus, after having attained an ascended Super Saiyan form, he was bound to be overconfident about his powers.
However, Vegeta's flaw in the Cell Saga also allowed him to grow as a warrior. Following his mistake against Cell, he never really underestimated his opponents and almost always tried his best to take down enemies as soon as possible. This change was evident at the end of the Cell Saga itself.
Vegeta, being a prideful warrior, would have never interfered in a fight. However, after realizing that his mistake would have cost him his son's life, he was willing to forego such feelings. This decision saw him interfere in Perfect Cell's fight against Super Saiyan 2 Gohan. Fortunately, this interference allowed Gohan to defeat Cell with his Kamehameha wave.
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