Life-cycle Approach to Competitive Advantage
I support the transient approach to competitive advantage.
The foundations thereof lie both in the internal environment (the organization dynamics and product performance), as well as in the external environment (the relevance of the product to the customers' needs, as well as emergence of other competing products, and services).
A CA can not be static in nature, unless you freeze these variables in time. Continuous observation of these dynamics, and responding to the changes through organization renewal and product improvements are making the competitive advantage evolve with time and with changing conditions.