A colleague of mine once told me a story that proves how small the academic world can be while underscoring the best reason to document sources: Doing so is likely to make you friends; failing to do so can only make you enemies. This colleague was asked to review a proposal submitted to the National Science Foundation, and was irate when he realized that an author of the proposal did not acknowledge my colleague’s work when he clearly should have. An investigation confirmed my colleague’s suspicions, which stung all the more because he had once actually nominated the author for an award. For my colleague, the author, and the National Science Foundation, this became an unpleasant situation all around, breeding distrust and embarrassment. A lot of time was wasted. All of this could have been avoided if the author had merely put his research into the appropriate context by properly acknowledging his sources. Instead, the author—whether intentionally or not—plagiarized, thus hurting other members of his proposal team as well.
When you write papers, you might be tempted to plagiarize to try to cover up the fact that almost all of your paper came directly from sources or that you relied heavily on the internet for your research. Your well-read professors will not be fooled by this tactic, though, and part of your job as a researcher and writer is to organize, assimilate, and recast your information in your own form. If you find yourself doing such things as using the same source for several paragraphs in a row or failing even to provide your own topic sentences for paragraphs, you are obviously not doing your job as a thinking writer. Do not fall back on the flimsy excuse that you might as well just copy it exactly as it appeared because you "like the way it was written." The context for your writing is different from the context of the original. The reason you use sources in the first place is to simplify and summarize information and weave it into the pattern of your own ideas, and your pattern of ideas will develop as you write and do your research.