There’s really nothing that can substitute for the certainty of actually watching someone struggle to use your design, but these analytical approaches are quick ways to get feedback, and suitable fallbacks if working with actual people isn’t feasible.
I like this sentence because it recognizes both the value and the limits of analytical evaluation. The author acknowledges that while direct user observation provides the most authentic insight, analytical methods still play a vital role when testing with users isn’t possible. This balance between practicality and depth reflects a realistic approach to design research. It reminds me that good designers use every tool available but never lose sight of real human experience.