This quote sums up the tribalism and "othering" that is the theme of Lamb's essay "Imperfect Sympathies," which is from his collection The Essays of Elia. In it, Lamb deals with the tendency of people to prefer the ways of their own people to the ways of outsiders. His narrative persona in the essay, Elia, states, for example, that he is
a bundle of prejudices .... In a certain sense, I hope it may be said of me that I am a lover of my species. I can feel for all indifferently, but I cannot feel towards all equally .... I cannot like all people alike.
Elia goes on to explain, sometimes tongue-in-cheek, some antipathies he has toward "outsider" groups in England in the early 1800s, including the Scottish (who were often looked down upon at the time as less civilized), Jews, Black people, and Quakers (a group he praises in other essays).
Elia begins with the Scots. The quote "I have been trying all my life to like Scotchmen, and am obliged to desist from the experiment in despair" acts as a topic sentence. It means he has determined he can't like the Scots despite trying hard to do so, and he then goes on to explain why. The explanation is illuminating in terms of describing Lamb's understanding of himself as an essayist. He contrasts the single-minded, almost brutally black-and-white views and strong opinions of the Scots (playing on stereotypes) with his own style. He, in the guise of Elia, is, half-jokingly, an "imperfect intellect" because he is "suggestive" in his thinking, meaning he is not so assured of the truth as the Scots, but content with "fragments ... hints and glimpses" of truth seen from "side face."
While Lamb criticizes the blunt honesty and self-assuredness of the Scots, he also criticizes his own tentative approach to reality, leaving it up to the reader to decide where the happy medium between the two extremes might lie. In the end, Lamb's essay is offensive to modern sensibilities but instructive in laying out how tribalism and prejudice work.