The core concept of Value refers to whether a solution is delivering the potential value that was expected, as well as the analysis that determines why the value may or may not be delivered.

In this case, the core concept of Solution and the core concept of Value are aiming to determine whether the value was delivered as expected.

In the example of Debby's Unique Dresses mentioned earlier, the additional website functionality still did not deliver the expected value of increased sales. It is the role of the business analyst to analyze the solution to determine why this is the case.