Recently, I was leading a training session for one of our clients on best practices for implementing designs using HTML and CSS. Part of our time included a discussion of processes such as style-guide-driven development, approaches such as OOCSS and SMACSS, and modular design. Near the end of the last day, someone asked, “But how will we know if we’ve done it right?”
At first, I was confused. I had just spent hours telling them everything they need to “do it right.” But after thinking about it, I realized the question was rooted in a deeper need to guide and evaluate what is often a set of subjective choices — choices that are sometimes made by a lot of different people at different times.
Source: Smashing Magazine The Nine Principles Of Design Implementation