When Should I Cite??
Bottom line, you should cite any time you are giving ideas that are not your own
Despite what you may think, it's perfectly fine to present an idea in a paper that isn't yours in order to support your own thoughts/ideas or arguments. Just be sure to acknowledge who came up with the idea, and where you found the source by using an in-text citation and the complete source information in the bibliography.
In fact, professors like when you cite others ideas because it shows that you put thought into your paper and you researched the topic thoroughly!