Terra is one of the three main protagonists featured in Kingdom Hearts: Birth By Sleep. He prides himself on his hard work and dedication to mastering the Keyblade. He is very close with his peers, Aqua and Ventus. Building to his mark of mastery exam, Terra makes clear how important attaining the title of Keyblade Master is to him, and it is apparent how hard he's worked towards it. However, at the end of his exam, he fails, on the basis of one of his mentors, Master Eraqus, sensing darkness in his heart. This distresses Terra, and he flees the training grounds, leaving Aqua and Ventus to go searching for him.
At the beginning of the series, Terra comes across as hardworking and loyal, yet his hubris is obviously his own downfall. He consumes himself in his own goal to become a Keyblade Master, leaving his heart vulnerable to the influence of darkness through his own negative emotions regarding his self confidence which he has hinged wholly on the mark of mastery exam. Throughout the series he has to confront and defeat not only his own disgraced mentor, but his own heart and mind. By the end of Kingdom Hearts III, Terra has learned to not be so hard on himself, and that his value as a person is inherent, and not something he has to earn. He vows to never leave his friends again, understaning that they love him for who he is and not what he is capable of.