When we're designing our route, we need to know what it's purpose will be, but there's something else we need to know as well. Who the route is for. I don't mean the name of some particular climber. Rather, the sort of climber for whom we are setting this route. This information is closely related to the purpose of the route, but it is a distinct question, and an incredible helpful way of providing a framework for our setting.
To help explain this idea, I'm going to help myself to another concept from the world of design. Personas.
In the context of indoor climbing and route setting, the use of personas are most effective when we're talking about the particular grade ranges, or colour bands - depending on how your gym sets routes. For examples sake, let's say your gym uses monochromatic grading. Purple, Blue, Green, Red, Black - with purple being the easiest, and black being the hardest climbs. When setting routes of each grade, you should have an idea of what climbers of each colour are capable of - technically, physically, and even psychologically. By climbers of each colour, I mean a climber for whom that colour is their limit. You can create a 'Blue Climber' persona. This might look something like the following:
Blue Climber: Understands foot matching, hand matching, rudimentary flagging technique, low physical strength (not capable of multiple pull ups, or dead hanging small edges), doesn't know how to utilise momentum, is proficient in basic route reading techniques.
Returning to our Blue Climber persona: With these restrictions in mind, when we are setting a blue route, we have created a framework within which to design the route. We simply need to ensure that we stay within the capabilities of the persona. If we do, we will be able to create a range of climbs that are roughly consistent in difficulty, and present clear distinctions between our colour bands. This manages the expectations of your climbers, and enables them to systematically progress through the colour bands. I'm not suggesting you pin up definitions of the 'Blue Climber' next to your colour coding chart. It's a hidden design process, but clarity here will absolutely show through in the overall structure of your routes and gym layout.
As the definition that I quoted above points out, it is very important to realise that this doesn't have to map onto a specific person, and it certainly doesn't have to be %100 true for every person climbing at this grade. Rather, it's an approximation of the capabilities that's drawn from observations from the whole population of blue climbers. Notice that these things can change, and they will. Maybe you'll learn that, actually, climbers at this level are capable of using smaller holds than you thought. Fine - adjust the persona, and tweak the style of those colour of routes accordingly. Or, perhaps we learn that the capabilities of the Green Climber are too far beyond the Blue Climber, which is resulting in people stagnating between these two grades and not progressing. Again, adjustment needs to be made. It's a dynamic, evolving process.
One big advantage of utilising this framework when setting routes, is that it prevents setters who are strong climbers from setting 'easy' routes that rely on capabilities that less advanced climbers don't have. For example, for somebody climbing V6, a long, dynamic reach off of two jugs and big feet to a bucket, is not a difficult move. For a climber of that grade, it feels absolutely effortless (and fun, to boot). If someone set this and was simply trying to decide difficulty based off their perception of how hard it felt, they could simply say, "It felt very easy, therefore it must be (for example) a blue difficulty movement." I've seen a lot of boulder problems and route's like this. They're basically V3's for V6 climbers. And yet, for somebody with the capabilities that were laid out above, that sort of move is very difficult. They will probably try to achieve the move statically, likely resulting in a complete shutdown. This is the issue with limiting the communication about grades to simple numbers. Instead, personas are a much clearer and more helpful tool for setters to use. Of course, sometimes the 'purpose' of your route or problem will be to teach climbers of a particular grade a specific technique, that stretches the technical limits of that grade - fine, in moderation and communicated properly. This is when creating a 'beta video', or direct communication with your customers is beneficial.
What's the skinny? When designing routes, try to have in mind the persona of a climber who is likely to be climbing the route. Set within the defined constraints of that persona, and you are more likely to create an effective product.