Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:While it must be acknowledged that the initial acceptance of e-books is an important step toward realizing the early success of this innovation, empirical evidence shows that the long-term sustainability of an innovation and its ultimate success rest on its continued use, rather than on its first-time use.(13,14) This is because the development of innovations usually involves a significant initial outlay of capital, and a lack of continued use of the innovation could jeopardize the organization’s ability to recoup the investment in the development of the innovation, contributing to corporate failure.
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