Build vs Buy Evaluation

Help me decide whether to build or buy for {{capability}} in {{context}}. Compare building it ourselves versus using a library, open-source project, or third-party service: the true cost of building and maintaining it, the maturity and risk of the options, lock-in, the importance of this being core to us, security and reliability, and total cost of ownership over time. Avoid both reinventing a solved problem and outsourcing your core differentiator. Recommend a path with the reasoning, and note the hidden costs people underestimate on each side.