Here's a breakdown:
* If you're summarizing information from a specific source (book, article, website, etc.), you absolutely need to cite it, even if you're paraphrasing. This is to give credit to the original author and avoid plagiarism.
* If you're summarizing information that is considered common knowledge, you usually don't need a citation. Common knowledge is information that is widely known and accepted, and can be found in multiple sources without attribution.
* If you're summarizing your own thoughts and opinions, you don't need a citation.
However, it's always good practice to err on the side of caution. Even if you're unsure if something is common knowledge, it's best to cite your sources.
Here are some additional things to keep in mind:
* The length of your summary matters. A brief summary of a complex idea may require a citation even if it's mostly in your own words.
* The purpose of your writing matters. Academic papers, for example, require stricter citation practices than casual writing.
Ultimately, the best way to determine if you need to cite something is to use your judgment and follow the guidelines set by your institution or publication.