Final answer:
In agile development, the principle of enhancing an existing product or process is not part of the Agile Manifesto, which instead emphasizes individuals, working software, customer collaboration, and responding to change.
Step-by-step explanation:
In the context of agile development, the principle that is not part of the core agile manifesto is "an existing product or process is enhanced". The Agile Manifesto emphasizes the following principles: "Individuals and interactions over processes and tools", "Working software over comprehensive documentation", "Customer collaboration over contract negotiation", and "Responding to change over following a plan". Enhancing an existing product or process is more of a general concept in product development and does not specifically oppose any agile principles, whereas the principles listed in the Agile Manifesto are a clear preference over the alternatives.
Sometimes, poor design decisions made early in the process will make it impossible to develop a design that successfully meets customers' needs. Agile methodologies, with their emphasis on incremental design and flexibility, aim to prevent such scenarios by allowing for continuous improvement throughout the development process.