To answer the question I think the concept of iteration is the most subtle to understand, just because at a lot of times, there is something spesific that we need back, and we are writing a specific loop to return it instead of exploring all the data or variables. that said I found myself using iterations to select a spesific value or check an array a lot of times. sometimes its fun just to explore and see if your logic is correct of what return is going to be displayed, in any case all of procedural ruby is important, I just find myself using loops a lot.
**Nothing is impossible!