Wikipedia:PRESERVE

is the product of millions of editors' contributions, each one bringing something different to the table, whether it be: researching skills, technical expertise, writing prowess or tidbits of information, but most importantly a willingness to help. Even the best articles should not be considered complete, as each new editor can offer new insights on how to enhance the content in it at any time.

Another way editors can improve an article is by finding a source for existing unsourced content. This is especially true if you come across statements that are potentially controversial. You do not need to be the person who added the content to add a source and citation for it.

Perfection is not required: . Collaborative editing means that incomplete or poorly written first drafts can evolve over time into excellent articles. Even poor articles, if they can be improved, are welcome. For instance, one person may start an article with an overview of a subject or a few random facts. Another may help standardize the article's formatting, or have additional facts and figures or a graphic to add. Yet another may bring better balance to the views represented in the article, and perform fact-checking and sourcing to existing content. At any point during this process, the article may become disorganized or contain substandard writing.

Fix problems if you can, flag or remove them if you can't. Preserve appropriate content. As long as any facts or ideas would belong in an encyclopedia, they should be .

Likewise, as long as any of the facts or ideas added to an article would belong in the "finished" article, they should be retained if they meet the three article content retention policies: Neutral point of view (which does not mean no point of view), Verifiability and No original research.

...
Wikipedia