I believe that the points made by Vitruvius’ Triad are all important, and you cannot have one without the other, or two without one. However, stability seems most important to me since without it, nothing can exist. Then I think utility is needed because without purpose, something is useless. Finally, beauty adds charm. It reminds me of the human body; one needs protection (stability) for body parts that have a specific purpose (utility), and beauty adds a nice touch.