To prove the importance of the JAK pathway, someone needed to discover a compound to test the hypothesis that inhibiting the JAK enzyme was of value in treating disease.
They were, despite that title, too kind to the hypothesis that the drugs under examination actually did have therapeutic value that a placebo could not duplicate.
Validating a hypothesis around whether or not a customer will find any value in your product, and iterating until you find the right product-market fit, is an approach that should extend well beyond the product development stage.