Every organisation using AI faces this question repeatedly, and the right answer changes depending on what you're building and when you're building it. The case for buying is strongest when the capability is well-understood, widely available, and not central to your competitive advantage - things like document processing, basic chatbots, or standard analytics. The case for building is strongest when the capability is core to your differentiation, requires deep integration with proprietary data, or needs customisation that vendors can't provide. But the decision isn't purely rational. Organisations with strong engineering cultures often default to building when buying would be faster and cheaper, while organisations without technical depth sometimes buy solutions they don't understand well enough to evaluate or manage. The best approach is to be specific about what you're deciding: not "should we build or buy AI" but "should we build or buy this specific capability, given our current resources, timeline, and strategic priorities?" And revisit the decision periodically, because the vendor landscape evolves quickly and what made sense to build two years ago might now be available as a mature, affordable service.