By "one aspect of life," it sounds like you're asking whether a novel can be quite singularly focused (instead of containing many characters and subplots). Let's think about a novel that would fit this category.
I would argue that Pride and Prejudice focuses on "one aspect of life," in that it centered around the inequalities of women in Austen's society that often left them with few options regarding marriage. Almost every other conflict centers around this "aspect of life," and Austen masterfully portrays the way these societal limitations affected various women in the story.
Another book that fits this classification well is The Outsiders. The main "aspect of life" that this work examines is the way societal divisions which focus on differences between groups of people lead to misunderstandings and even violence. All of the central characters of this work are caught up in the conflicts surrounding class differences in their town.
Most often, stories are classified according to their length, regardless of how complex the plots and conflicts are. Novels generally exceed 40,000 words (and can be much longer), while short stories often contain less than 7,500 words. There are some incredible short stories out there that focus on a singular "aspect of life," but works like "Thank You, M'am" or "The Story of an Hour" could not be classified as a novel, simply because they lack the length necessary for that designation.