Optimize at scale, not for scale - Don't optimize for scale

Most of my work is in building MVP's and greenfield projects, and the most common technical concern I receive is "Will it scale?". The very mention of that question can spur pretty heated debates. Should we build an Express server, or go with Serverless functions? Do we use PostgreSQL, MongoDB, or DynamoDB? Should we put everything in a vm and scale vertically, or should we Dockerize everything to make horizontal scaling easier? Should we use Ruby+Rails, or maybe Elixir+Phoenix? Should we build our own auth system, or use Firebase Auth? Hopefully I'm not offending anyone by making these comparisons, I realize there may be some false equivalencies since not all projects are the same, and every technology has it's sweet spot. But, many developers have to grapple with questions like this every time they start a new project, myself included. Many teams fear "The Big Rewrite" Very few large companies are still running on the infrastructure they started with.