When you consider performance from the very beginning, it is cheaper and quicker to fix issues. This is true for most problems in software development. The earlier you catch a bug, the better. The worst time to find a bug is once it is deployed and then being reported by your users.
Performance issues are a little different when compared to functional bugs because often they only reveal themselves at scale, and you won't notice them before a live deployment unless you go looking for them. You can write integration and load tests to check performance against your specific quantified goals, which we will cover later in this book.
