Ethical researchers respect the intellectual property rights of others.
As you do research and create your own research paper, report, web page, or other product, you may use resources created by others. Each of the sources you use must be credited. Not to do so is to commit plagiarism, which is both unethical and a serious infraction of the student codes of virtually all colleges and universities. Unfortunately, many students commit plagiarism unintentionally. Therefore, so long as I paraphrase someone else's idea, I need not credit its source.