The involvement of Trabb's boy in Pip's rescue from Orlick is an example of irony.
The above question has been asked from the novel “Great Expectations” by Charles Dickens.
Trabb's boy had earlier mocked Pip in the public and had brought him great embarrassment. Therefore it becomes ironic that he should be the one who will rescue Pip. Hence, Dickens uses such strategies in his novels in which he places people of good characters with bad traits and vice-versa.
