I am God's lonely child

De Niro in Taxi Driver

There's a shit load of anger brewing inside a person who finds himself lonely. It probably comes from a sense of feeling discarded by society. Or maybe his own ineptitude to make genuine good connections with people. That's what is so beautiful about the movie. His social awkwardness. His inability to be a seducer. Taking a girl you just met to a C grade film by accident. Hating yourself for the stupid shit you do. Talking to yourself in the mirror. Imagining yourself with guns, lots of guns. Lots of shooting random assholes, lots of scenarios where you pull up a firearm on an unsuspecting bastard trying to screw with you and pump bullets into his shady ass. Pride. She offers him money at the end of their last cab ride and he drives away. Savings. Being lonely sure makes you save a lot of money. Insomnia - the absolute hallmark characteristic of a lonely person. No sleep. Watches porn in cinema halls to while his time until the next morning. Thoughts of self harm. Fidgeting with the furnishings, electronics especially. Anger and distress when something breaks/ malfunctions. 

Most important - the craving to do good by society in spite of it all, in spite of himself. Self-preservation as an instinct rising above all else. Travis tries to kill the minister but fears getting caught and so runs away to the brothel instead where he wants to save Iris from the mafiosi and her pimp. So he kills them both, and finally does become a hero. That's his redemption. A simple taxi driver's redemption. He's no big shot, he's a simpleton. He's got no big ambitions, no grand goals. He's got a simple idea of life, of love, of death, everything. He becomes a hero to Iris' parents and that's all he needs. To be a hero to somebody. So what if he couldn't be a hero to Iris who herself had grand political ambitions. He becomes Iris' grand saviour. Pins up her parents' letter on his walls. Goes right back to his normal life. 

Writes a journal chronicling his taxi driver thoughts. Very introspective. Very self-aware for a taxi driver. A guy who isn't very highly educated but means well. Alluding perhaps to smart people who for whatever reason are living lower lives than they ought/ deserve to. There's such a huge chunk of them in this world. Or maybe it's just a state of mind from which some people are unable to come out. In which case the movie is brilliant. Ah, it's brilliant anyway. It's a phase in life during which your state of mind is like the taxi driver's. Some people get over it clean, others feel the need to do things to become heroes.