Product people ignore scalability at their peril. Think about it: A prototype of your product may be produced relatively quickly as long as there are only a few users on the system at a time.
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On the other hand, a system can theoretically be designed to support almost any number of users, but it will take proportionately longer to design and develop. Which are you aiming for? You can't have both.
If you are specific about how much usage you expect at what stage of the product’s life, you and your development team can find a balance between these extremes for each stage of your product's life, reducing the risk of failure without overengineering the solution.
How does your organization deal with scalability? Tell me a story. (And do not tell me you leave it to engineering to worry about.)