The 2 most important reasons:
- Citing sources allows for the open exchange of ideas. You can expand your own research by consulting sources that other people have cited, and they can do the same with the ones you cite. This is the basis of scholarly communication.
- It is illegal and unethical to use someone else's words or ideas without giving proper credit. Failing to give credit is plagiarism, a serious offense that usually results in severe penalties on any college campus or in the scholarly and corporate worlds.