In this position paper we discuss the application of personalization in persuasive technology design in light of the Personalized Design Process model (PDP-model). The PDP-model defines personalization as aligning a persuasive product to the end-user by stakeholder involvement (i.e. designers, endusers, domain experts and family/relatives) across the Problem Definition-, the Product Design- and/or the Tailoring design phases. It is expected that personalization in a PDP enhances the motivation of end-users to interact longer and more frequently with a product, increasing the likelihood that the product will reach its aimed-for effect. Although personalization in a PDP is a common method in persuasive product design, its added value has not been sufficiently validated by scientific research. We propose several reasons for the frequent use of personalization in a PDP, despite the lack of evidence for its added value. Furthermore, we discuss how personalization could be validated according to the PDP-model.