One of the major risks in software development projects is the phenomenon of Over-Requirement, also known as over-specification and gold-plating, where a product or a service is specified beyond the actual requirements of the customer or the market. We argue that Over-Requirement is partially due to the emotional involvement of developers with specified features, an involvement associated with the IKEA or the I-designed-it-myself effect, which implies that people come to overvalue their creations when successfully designed or constructed by them. To investigate this argument, we conducted an experiment in the context of software development in which over 200 undergraduate students participated. The experiment required participants to complete a specification task and measured the change in perceived valuation of a specified nice-to-have feature, by measuring it before and after its specification was completed. The experiment results confirmed the existence of the IKEA effect and its influence on Over-Requirement. The results also imply that the IKEA effect in software development is multifaceted where the level of specification difficulty, whether objective difficulty (in terms of constrained specification duration or unconstrained specification freedom) or subjective difficulty (as reported by participants), affects the magnitude of the IKEA effect.