The goal of a license is to help inventors monetize their patent rights. Oftentimes, inventors wish to start by licensing their technology without every manufacturing and selling their product. Although this sounds attractive, these types of deals are an exception not the rule. More often than not, to secure a license deal, the inventor has to manufacture and sell their product to show that there is a market demand for their idea. This way the prospective licensee can see that they are paying for an idea that has a demonstrable market demand. The further along the business development cycle you can take the idea, the greater the likelihood of securing a license deal.
Moreover, not all license deals are good. Some drain the resources of the licensor and can shift a substantial amount of risk to the licensor. Others can trap the licensor with a particular licensee. To avoid these types of problematic situations, safeguards are placed in the license agreements. These include performance milestones which allow the licensor to terminate the license if the licensee is not meeting their commitments.