The whole reason why medical devices, or products in general, are created are to fill a users need, and that need will be heavily researched prior to the initiation of the project, think back to the initiation stage. If you come to the validation stage of product development and your inputs are “abc” and your user needs are “xyz” (very far off) then you would have to reevaluate your methods or your design so that it will meet those user needs in the future. Validation will show you how the product works in the real world situations and if it can actually perform the way it is supposed to. Many things can effect the end product in ways you may have not foreseen, for example minor changes early in the development process may have a domino effect leading up to an unintended compromised device/user interaction, but I don’t think compromises will be made intentionally (if that is what the original post was implying).