Continuity mistake: When Travis is with the gun salesman, he is trying out the black gun. You see a close up shot of him holding the gun with his arm outstretched with his jacket on. In the very next shot (no time has elapsed) his arms are at his side and his jacket is now completely off. (00:56:50)
Travis Bickle: Loneliness has followed me my whole life, everywhere. In bars, in cars, sidewalks, stores, everywhere. There's no escape. I'm God's lonely man.