The entire goal of the "Nail It" phase of the Nail It Then Scale It method is to identify what you think may be a monetizable pain, test it with customers, and determine whether your assumptions were right or whether you should try a different pain. By the end of the "Nail It" phase, you should have a tested and validated monetizable pain. But at this stage, the pain you identify is just a hypothesis that will need testing.
A Monetizable Pain Hypothesis is a clear description of your hypothesis of what pain the customer is experiencing. To put it simply, what do you think keeps your customers awake at night? What do they consistently struggle with? A Monetizable Pain Hypothesis might look something like the following:
"Individuals don't have a way to to connect to other individuals in a world-wide marketplace to buy and sell their goods" (eBay).
"Businesses have no way to measure how effective their digital, online marketing is" (Google Analytics).
"IT Help Desk managers can't do their jobs effectively because their front-line employees cannot share knowledge and information in an easy way" (Knowlix).
"Busy moms wants their children to eat healthy, but they're too busy to cook or stop at healthy sit-down restaurants" (Subway Restaurants).
"Wealthy, frequent business travelers dislike the airport experience, but don't have enough money to purchase a private jet" (Surf Air).