The free dictionary explains the saying "don't send a boy to do a man's job" as;
"Avoid assigning challenging tasks to those that are inexperienced or otherwise incapable of completing them."
Sometimes this is easy to avoid - it's clear that a new recruit isn't up to speed yet. Other times however, it's not so easy... they're a mature staff member, you've poured a lot of training in!
This topic is of course, the matter of delegation. Delegation has had a lot written about it; that it's a vital part of management, how to make your expectations clear, how to check for understanding, etc, etc. Something that has been overlooked as far as I can tell however, is the difference between how you and they are wired and, whether or not they should be delegated the task at all.
The question I am posing here is; was the subject a good match for the job in the first place? Perhaps they were just too different?
It seems to me that when we're not under pressure we do often consider the suitability of a person to given task. If we're organising a social community event for instance, we might consider "who would be good at welcoming people" or, "who would be good at sorting out the music." But all too often we seem to forget this soon after employing people. Instead we default to; if a person has been employed to do a job, and this thing is part of that job (or most suitable for a person in that job), then they need to be able to do this thing as well.
But.. how good a match are they really?
Now, everyone knows that we're all different but there seems to be an assumption that these differences are crossable with "clearer" communication. One is encouraged to have subjects repeat back instructions, or simply to be given the desired outcome and let them get on with it, and so on. The question has to be asked however, how is that working out? Where "clearer" communication ends up simply being more forceful communication, this should be seen as a sign that perhaps they don't get it.
Point to clarify; whilst someone might possess the potential in their personality trait, they must also have the corresponding character you require for the job you are wanting to delegate. A lack in either area would rule them out.
Anyways, all of this makes me think that actually, crossing that difference between people should not be so quickly overlooked. That being clearer in our communication may not bring the results we hope for [in our delegation].
If someone is properly very different at their core, maybe we should "avoid assigning challenging tasks to those we know (if we can be honest enough to admit) are incapable of completing them (to the standards we want for that task)."
To do such a thing would be to send a boy to do a man's task.
Proposing this might seem to imply such a person is "lesser" but I challenge that. I think it just means that there is a difference between two people. And a difference between people does not imply that one person is "better" than another, doing that would conflate "value as a human" with "suitability for a given task."
The point here is that if you really want a job done just so, giving that job to someone who is really not wired in way that would naturally produce that is a difference not crossable with clearer communication. Give the job to someone who does naturally think that way. And yes, at times this may mean doing the job yourself (ie; the job is not delegate-able) or otherwise adjust your expectations.