Market is often hidden behind curtain. Your job is to discover (often hidden and) unmet needs and wants of customers not to invent them.
Market itself is whole sum of WTP (Willingness To Pay) of customers when you solve the customer’s problem. So you can estimate your potential market size even when you don’t have concrete solution ideas yet.
Like this. Market Size = WTP of one customer when problem solved * number of customers
Market is equal to the sum of customer’s problem.