The business world is one example where first impressions matter. When interviewing for a job, the way you look highly impacts the likelihood of you getting the job. Although your knowledge and experience also play a big role, the employer will always pick an intelligent, well-dressed man over an intelligent, under-dressed man.
In Mark Twain's Huckleberry Finn, Tom Sawyer did not let his social standing rule his life. Although he lived with his aunt, who was rich, he refused