Mark Bjornsgaard has scaled and exited seven businesses in healthcare, finance and music. As founder of Deep Green, Mark has worked out how to turn waste heat from AI data centres into heating local infrastructure and homes, with billions of investment. In this conversation, Mark talks through the long road to making that idea commercially viable, why earlier versions failed, and why the real breakthrough came from solving an economic problem rather than leading with a green one. He is refreshingly direct on what it takes to build: kill weak ideas early, stay obsessed with the customer problem, and make new systems real enough that people can trust what they are seeing.