In John Steinbeck's Of Mice and Men, the main characters are George and Lennie. We know that they have lived together most of their adult life and that George is basically Lennie's caretaker even more so than just being his friend. The reason for this is because Lennie has cognitive problems that affect his social skills. He has a strength that he cannot control which has led to the accidental death of some animals. Lennie also has a tendency to speak out of place, say unintelligent things, basically betraying the fact that he is not very smart.
Therefore, when George spoke on Lennie's behalf he was desperately trying to ensure that Lennie would not speak and give away the fact that he was different, with a simple enough mind, and that he wouldn't be hired for that reason. Plus, they would also judge George by association.