As Kent he can never save lives. Superman maintains a total separation between his two selves and this allows Superman to avoid any incongruity between his two identities. Kent remains the newspaper nerd, never hinting at what he is physically capable of. His ability to keep his double hidden from the world becomes evident when he is still in school and manages to resist capitalizing on his strength to become the school's starring quarterback or on his hyper-masculinity to get girlfriends. Kent keeps his double hidden from the world just as Superman keeps his mundane identity secret. Superman never sullies his image by wearing a monkey suit and does not appear weak even in the face of doom or disaster.
The only time Superman compromises the integrity of his double identity is by getting close to Lois Lane. In fact, she begins to suspect that Clark Kent might indeed be Superman when it dawns on her that the two have never been seen together. She quickly dismisses the thought as absurd, though, because Superman so artfully crafted his double. The differences between Clark Kent and Superman are sharp enough to help him avoid conflict. Yet Kent can change into Superman and back instantly and with little effort. The ease at which he can transform back and forth between Kent and Superman mirrors the fact that the double identity is superficial only. Beyond the externalities of his physical appearance, Kent and Superman are the same person.
Lex Luthor facilitates the development of Superman's powers, providing the superhero with a primary purpose. Kal-El told his son that he would be fulfilling a specific function as a super-being on Earth and that his powers would be put to good use. Kent therefore develops his double identity with his higher purpose in mind, sublimating his powers for the greater good of humanity rather than channeling them into mundane possibilities like wooing women. His double neither helps nor hinders his goal, but if Superman had never cultivated his alter-ego as Clark Kent he would never have met Lois Lane and would have been truly alone and without friends. Although he can never fully reveal himself to Lane, Kent's identity allows Superman to at least pass for being an ordinary person.
The idea of the double is also developed in Superman through Superman's arch nemesis Lex Luthor. Unlike Superman, Luthor has no personality double. He is a proud, unapologetic criminal mastermind. Luthor does not hide behind a double life and does not mask his evil intentions behind a day job. His pride stands in direct contrast to Kent/Superman's humility. Even in his cape when he prevents a plane from crashing, a train from going off its tracks, or when he catches Lois Lane mid-air, Superman does not brag. Without a double, Luther seems all the more evil. Luther doesn't even pretend to be good. If he were to create a double personality it would not be a reflection of his true self, like Superman's double identity is. No other character in the movie Superman has a double identity like the title character does. This allows the filmmakers to let Superman stand out clearly as the hero.
Superman's double serves him well, allowing him to fulfill his higher purpose on earth as a fighter for "truth, justice, and the American way." He uses his identity as Clark Kent to enable him to form social ties and to network with human beings. Superman creates as plain an identity as possible to avoid being detected and minimize the possibility of suspicion. At the same time, his identity as Clark does not conflict with his identity as Superman. Both Clark and Superman are honest, kind individuals. However, his double identity prevents both Clark and Superman from enjoying an open relationship with Lois Lane. The primary romantic storyline of Superman is nearly built on a lie. Lois Lane falls in love with Superman but not with Kent. In fact, Kent irks her. The film raises questions about the nature of love, given the fact that Lane doesn't embrace Superman's double the same way that she embraces Superman. However, Superman is the core identity of the film's protagonist and therefore Lane does fall for the real…