Rather than "crowding out" private investment in medical research, as some skeptics of government support contend, public and private medical research are in fact complementary. Basic, early-stage research expands the science knowledge base, laying the foundation for later-stage research and innovation in the future. This is dynamic nature of innovation. Government's role is especially useful early in the process. Although substantial, the benefits of basic research are reaped over the long term and are often shrouded in uncertainty. Because of this, firms tend to forgo basic research in favor of more applied research and development using existing ideas with more discernable, short-term rewards. Public funding addresses this reality by helping to refill the knowledge pool from which firms draw commercial innovation.