I sometimes run into entrepreneurs who are very focused on making sure that they have the infrastructure to meet demand. They don't want to disappoint their users or damage the reputation of their startup. Those are both very worthy goals.
But this loses sight of an important fact: Don't worry about demand spikes--worry about if there is demand!
Figuring out how to deliver a service is a puzzle; you know that there is a right answer, and given some time and effort, you know you can solve it.
Figuring out whether delivering a service is worth it is a mystery; you don't know if there is a right answer, and you don't know whether or not you'll be able to find it.
Focus on the mysteries, not the puzzles. The mysteries can sink your startup long before you run out of fun puzzles to solve.