A related issue is also focusing so much on the tech (and often how well the product/service can scale) that you forget to do much marketing and end up delaying

A related issue is also focusing so much on the tech (and often how well the product/service can scale) that you forget to do much marketing and end up delaying the product/service for months as a result. Or worse still, never actually finish building it at all. Definitely follow the old get it working, then correct, then fast methodology, at least for projects without many billions of dollars in resources.