If a psychiatrist/therapist were to read only one poet, I would propose Dickinson, who takes in the exaltations and debasements of human experience like no other. But if one could read only one fiction writer, I can think of none better than Chekhov, who contrastingly explores the great and ordinary middle range of humanity. They complement one another well, Dickinson covering the remote ends of the bell curve and Chekhov covering the wide middle. In fact, Chekhov's persona--unpretentious, exacting, detached, unsparing yet humane--is exactly what one might hope for in a great therapist and diagnostician of the soul. "Ward 6" is a dismaying, even terrifying exhibit of the perils both of madness and of the medical profession, but I wish that every medical student and therapist in training could read it.
But there is no Chekhov story that is without its humble yet transcendent insight. This morning I reread one called "The Teacher of Literature," and at the end I had the wonderful thought that "This isn't fiction at all, this really happened just so, and I was merely a fly on the wall." It had the two necessary ingredients of great literature: strangeness (different century, alien culture) and absolute fidelity to reality.