Wikipedia:An article is the sum of its parts
 | This is an essay. It contains the advice or opinions of one or more Wikipedia contributors. This page is not an encyclopedia article, nor is it one of Wikipedia's policies or guidelines, as it has not been thoroughly vetted by the community. Some essays represent widespread norms; others only represent minority viewpoints. |
 | This page in a nutshell: The impact of any individual contribution should be considered in regards to the tone and perspective of the article as a whole |
The collaborative nature of Wikipedia encourages the rapid acquisition and integration of content from many different sources and viewpoints, properly weighted. While this tends to ensure that all relevant content is included in the article, it can also lead to articles that are poorly structured, include disparate and irrelevant details, overweight one or more minority viewpoints, and degrade the overall quality of the article.
Individual pieces of articles are what most editors seem to edit.
The problem is an article is the sum of its parts and thus editing single sections, no matter how important they seem to an editor, frequently results in a very ill-weighted article.
This has been a major problem in biographies of living people to be sure. All too often, editors with a particularly strong interest in a topic would seek to promote the subject (if they happen to like him) with all sorts of side statements, or, conversely, to denigrate those whom they do not like. WP articles with extensive "This person was evil" sections are often the result. (Sometimes the section is "This person's sex crimes", "This person's controversies" or "This person's hatred of some particular group" whether or not there is any basis in fact for the claims.)
Other areas where this syndrome is found are political, sociological, racial, and sexual articles, just to name a few.
If you find yourself adding to a section not because it is underweighted in an article, but just because you find it "important" – step back a little. Even add an edit you "disagree" with. Remember – articles are the sum of their parts!