The protagonist of Chekhov's short story, a cabman called Iona, has recently experienced a sad bereavement. As he tells his latest fare, a military officer, his son died about a week earlier. He'd been in hospital for three days before he eventually passed away. In response to a question from his fare, Iona says that he doesn't know exactly how his son died but that it must've been from fever. In any case, he says that his son's death was God's will.
On the face of it, Iona seems quite stoical for someone who's just lost his son. But that's just a façade; inside, he's hurting like you wouldn't believe. So much so, in fact, that he cannot be alone; it simply makes the pain a whole lot worse. Even spending time in the company of obnoxious clients is better than being by himself.
Iona feels that the best way of dealing with grief is to talk about it. Using his own primitive brand of talking therapy, Iona tries to deal with the loss of his son and the immense grief it has brought him by talking to anyone who'll listen. And not just anyone, but anything, as Iona ends this sad little tale by pouring his heart out to a horse.