In today's publishing world, it is very easy for an author to lose copyright of his works when signing publisher author agreements. In fact, most author agreements require that creators sign away all of their copyrights to the publisher.
Signing such agreements has very negative impacts on the author's reuse of his works. In most cases, after signing away his copyrights, the author can no longer use the work to make derivative works from it. The author cannot upload this work to a green open access repository or on social media sites, such as Academia.edu and ResearchGate. He also cannot share his work with colleagues or students and in all cases, the publisher has right to reuse the work in anyway that it sees fit. The author has lost all legal control of the work.
For more information, see the Author's Rights guide from Cornell University
Section 106 of the U.S. Copyright Law defines the limited exclusive rights of the copyright holder as being the ability to:
What this means is that creators of original works have the right to reproduce the works, make copies of the works, revise the works, perform the works and receive monetary gain from them.