What made Mr. Otis write a letter to Mr. Canterville informing him that the ghost had gone away ?

In Chapter Four of "The Canterville Ghost," Mr Otis writes a letter to Lord Canterville in which he conveys his family's belief "that the ghost has gone away." The Otises believe this because they have not seen the ghost on his "nocturnal expeditions" for some time. 

What Mr Otis does not realise, however, is that the ghost is simply in hiding. He has been humiliated and defeated by the Otises at every turn. On his...

In Chapter Four of "The Canterville Ghost," Mr Otis writes a letter to Lord Canterville in which he conveys his family's belief "that the ghost has gone away." The Otises believe this because they have not seen the ghost on his "nocturnal expeditions" for some time. 

What Mr Otis does not realise, however, is that the ghost is simply in hiding. He has been humiliated and defeated by the Otises at every turn. On his last appearance, for example, the ghost was making his way to the library to check on the blood stain when the twins leapt out at him, "waving their hands wildly" and shouted "Boo!" The ghost ran away in the direction of the staircase, only to find Washington Otis waiting for him with a large "garden syringe." The ghost, "hemmed in all sides" was forced to retreat into a fireplace and the incident left him feeling in a "terrible state of dirt, disorder, and despair."

The ghost thus felt unable to fulfill his duty of scaring the residents of Canterville Chase. This prompts him to remain in hiding, for fear of another assault by the Otises. Of course, the ghost is still at Canterville Chase, unbeknownst to the family, and is simply nursing his wounded pride. He will only leave Canterville Chase when the prophecy is fulfilled and he receives redemption for his sins.