Duende has several meanings. If we view it as the art of perfection, as I describe it, then at Wiki you will find the folllowing explanation: "A difficult-to-define phrase in the Spanish arts that connotes emotion and authenticity". Clearly, this closely relates to the competencies of the architect.
Some examples as I found them, for you, as to experience what Duende may do to you.
From the movie "El Amor Brujo" as created by Carlos Saura, based on music with the same title by Manuel De Falla, the following "Flamenco ballet". Here, I find there is a lot of silent emotion that you receive from a perfect flamenco dance, featuring professional dancers Antonio Gades and Cristina Hoyos. And the singing adds much to the experience.
And Delerium has the song "Duende". Here I see many symbols that are not known to me (yet). So this example, for me, closely relates to the knowledge of the architect. We all learned that 1 and 1 makes 2;-) However, in my childhood I was told that sometimes "1 + 1 > 2", viz. that the whole is greater than the sum of the parts. For example, that 2 connected people will have more knowledge than the sum of the knowledge each has by way of simple addition. Communication is the extra factor that makes this happen. An architect cannot know everything (as Aristotle already perceived). Instead, an architect knows where to find relevant information very quickly. So, an architetct is a knowledge worker, embedding knowledge management principles (how to handle knowledge) in all his activities.
Here is another example why "knowledge" is complex matter (as was explained to me early in life). That what you know at some point in time, can be mapped to the inner area (surface) of a circle. And when you get older, the circle grows as you gather more knowledge along the way. However, the lenght of the boundary of the circle (it's circumference) is the boundary to the amount of knowledge that you don't know. So, paradoxally, the more you know, the more you know there are things that you do not understand (yet).
Summarizing, architecting (developing architectures) is both art and science. As in art, they know what they should do from learning. As in science, they do what they know from experience.