Why Speed Matters

Picture this: you build a deduplication step for a data pipeline. During development, it runs against ten thousand rows and finishes in three seconds. You ship it. Weeks later, the table grows to ten million rows and your pipeline does not just slow down -- it takes thirty-five days. Not thirty-five minutes. Thirty-five days. Nothing in the code changed. The data changed. And the code was never built to handle it. This is the problem that Big O notation solves. It gives you a way to predict, before you ship, whether your code will scale or collapse. Big O does not tell you exactly how many seconds something takes. That depends on your hardware, your database engine, and a hundred other things. Instead, Big O tells you the shape of the growth: when the data doubles, does the work double, qu