Masashi was always praised by the elders of his clan for his aptitude in the Shinobi way and arts. By age 6 he had a rather large head because of it, and wasn't afraid to show off his skills to anyone who would watch. Having lost his father at the age of 3, maybe it was the need to be noticed by others because his mother was always busy trying to support them. Maybe it was because he really did have an insatiable ego. Who knows? All that is known is Masashi, because of his ego, was ostracized by the kids in his own class. They wanted nothing to do with the attention-hogging boy. It didn't take long until Masashi truly realized he was lonely, and realized that, though he had been grasping the fighting side of his clan's practices, he had been neglecting the meditation aspect. And because of that, he didn't have a single friend. It wasn't too long after that he began to meditate, mulling over his very short, yet loud, life. He realized all the principles his clan had built and their significance. It wasn't a short process. It took him three years until he finally reached a point where he realized that he needn't be loud and brash.
The transformation that came from it was something that even he couldn't believe. His entire demeanor and outlook on life and the Shinobi ways changed. Being a Shinboi, he came to understand, had nothing to do with displaying one's power, and being the best to be revered. No, it was about being the best so one could serve as the immovable wall and earth to protect loved ones from the evil that would seek to harm them. Once Masashi grasped that, he became more at peace with himself. He would continue to get better to protect his village, and only for that reason. It seemed that, once he came to that conclusion, the universe threw him a curve-ball that he didn't expect. Other students noticed his change, and the significant drop in decibels of his voice. They saw how he wasn't all about himself anymore, and was now more calm and serene. No longer ostracized, it was like all of his pent-up longing for friends burst forth. He was a very friendly person, and his friendliness was reciprocated. Even his fighting technique and jutsu improved.
It seemed that Masashi Kimura, despite his young age, had found himself and his Shinobi way.