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Personas must be:
Relatable: You want your team to relate to the persona almost as if it is a person they know.
Concise: Put only those details relevant enough for your team to design and build features for the product.
Well-researched: Start with a blank slate, perform market research, float surveys, conduct interviews and validate them with your team.
Well-structured: Structure your findings to create a story. This will put the team and stakeholders in the user’s shoes.