It depends on what you do. Scalability is about building a system to handle ten fold more traffic than it's seeing now; <10 is too little, 100 is over-engineeri

It depends on what you do. Scalability is about building a system to handle ten fold more traffic than it's seeing now; <10 is too little, 100 is over-engineering (and nearly impossible). Now imagine a graph data structure (any site with a news-feed/following functionality). You can get 10x increase in edges without a 10x increase vertices. Some kind of products also increase in usefulness (and demand) as they increase in user growth, so solving scalability problems is necessary to their success. It isn't, however, sufficient.