You've just cloned a unique cytokine named "zorf," then had the additional good fortune to publish your discovery in a top-tier journal. Your lab is the only source for this red-hot reagent. Within days of publishing the paper, you get a request for zorf from the Smith lab, which wants to test its effect on T cells. Publishing a paper in many journals obligates you to provide any unique reagents described in the article to researchers who request them. Such a requirement is entirely appropriate; without it, there might be no way to confirm a novel scientific finding using a difficult-to-obtain reagent.
You send the material to Smith straight away. A few days later, you get a new request for zorf from the Jones lab. Jones also proposes to test the effects of zorf on T cells. Sending zorf to the Jones lab could easily, in effect, pit the Smith ...