Sam's letter is a fine blend of both reality and fantasy. Explain.

The psychiatrist of Charley called him having a waking-dream-wish-fulfilment. Since the Third Level was all his fantasy, his wife Louisa too asked him not to look for the Third Level anymore. The narrator took to stamp collecting. One day while looking through his worthy collection, Charley noticed a “first day cover” which he believed not to have seen before. This cover was addressed to his grandfather and mailed to him at his home in Galesburg. It was on July 18, 1894. Definitely his grandfather must have put it in his collection and the same must be lying there since long. Since it was a “first day cover”, consequently, it was not opened.
There was a blank paper in it. By chance Charley opened it. On opening it was found that it had a letter from Sam. He had reached Galesburg and was living very happily. He had found the place very charming, peaceful and serene. It was also written in the letter that Charley should come to Galesburg and look for the Third Level. In other words, the letter appeared to be Charley's imagination like his escape into the Third Level. The psychiatrist too had warned him that his stamp collection was a mode of escaping into the past.