Specifications for manufactured systems inevitably change after systems are built and delivered to customers (engineering change). This might be due to errors in the original specifications leading to product failure or unintended negative consequences, feedback from customers on problems or new features, competition from other producers, new ideas for product improvement, or new products adapted from existing ones. The need for post-production changes is reduced with more adaptable systems, but increasingly complex products, shorter product lifecycles, and faster technological innovation make it impossible to completely predict how systems will need to change.