You can sell the piece as a reprint, to an anthology, or even sell the movie rights. If you sell all rights, however, you lose the ability to resell that material to any other publisher, ever. You can't sell it as a reprint, or to other countries, or even post it online on your own website. What you do NOT lose is your copyright. All you have sold are the rights to that specific form of expression.
New writers can be particularly vulnerable to demands for all rights.
Several recounted their own experiences and regrets. The publishers did a wonderful job, the book looked great, but it was like giving a child up for adoption. I don't know. No, but I'm not as desperate now as I was then. Getting your foot in the door is hard.