From the Diary of K.I. Chukovsky :

25 December 1964
Walked with Sima Dredden. He told me a wonderful, meaningful story. An intellectual settled in a railway guard's cabin. The guard was illiterate. The intellectual had great difficulty teaching him literacy. The guard was dumb, but eventually overcame the beginnings of grammar. He wanted to be a driver on the train. To do this, you had to learn dozens of rules on hand - and pass the exam. Intelligence has helped here. The guard became a guide, coming to the south, purchasing oranges and so on. It was sold in the north. and rich. Intellectual was arrested. Having spent his time in the camp, he returned home. Here he was rehabilitated - and showed his "case". It turned out that, after learning literacy, a grateful railroad driver first wrote a note on him: "I warn that NN has connections with abroad."