Thanks, Friction. Yes, I'm familiar with that saying. I guess it's the "do one" I'd like to see evidence of.
I'm an experienced enough teacher to know that even the brightest PhD student or the most skilled tech will, occasionally, run into an assay or technique that they can't do after seeing it once: they need extra training. And not every PhD student or tech is top-notch; the occasional individual is going to need a huge amount of hand-holding on a regular basis. So after they "see one" by watching me do it, I make danged sure they can "do one" before I let them loose and "teach one" to someone else. IMO it would be very poor scientific practice to assume that because they've seen it done once, they're accomplished enough to do it correctly themselves *and* to teach someone else to do it.
And that applies to each assay and technique. Just because someone's good at running Western blots doesn't mean they'll know how to do an ELISA. Expertise at ELISAs doesn't necessarily translate to primary cell culture, or microdissection, or flow cytometry. Similarly, there are a number of aspects to the craft of writing, and being good at one doesn't mean the author is good at them all. I'm sure we've all seen brilliant plots with cardboard characters, or shining settings with inadequate dialogue, or prose that sings in a plotless story.
I'd compare becoming a good writer to getting a PhD: it's a long hard slog, it involves mastering a large number of skills and techniques, and it's not something anyone else can do for you. Watching someone else get their PhD isn't the same as doing your own dissertation. And it's very unlikely that a university will hire you as a tenure-track academic and let you train PhD students unless you've got your own PhD.
You've let us know that you did the "see one" by hiring external editors. My criterion for the "do one" would be "published with an advance-paying press that is recognised as an accredited publisher by a standard author's group such as RWA, SFWA, HWA, etc."
Sorry if I'm being clueless, but I'm not getting it. Because if you're not competing with N Griffith etc, what niche are you filling? Why would someone pay thousands of dollars to you when for the same price they could get an established, accomplished editor? Why would they pay you to edit their first few pages when Nicola Griffith will do that for free?