This very topic has crossed my mind MANY MANY times. I see it slightly differently, as instead- how do aquarists define "success". I have seen both extremes. Some claiming such in honestly weeks, whereas others in numerous years. Some by breeding success, other by getting the animal to eat.
IMHO, and IMHO ONLY(!!!), I think no animals should be acquired without considering the duration of ownership, growth, dietary considerations, amongst other things. A close second to horrific things for me to hear (second to only calling clownfish and Hippo tangs "nemo" and "dory") is hearing the absurd and comical phrase (upgrade planned", or "bigger tank in the works". I cannot understand why someone would buy fish, particularly commonly available fish, in such a rush, apparently KNOWING they are not suited to house them currently. Acanthurus tangs, Pomacanthus Maso tangs, etc are purchased, and all too often, the purchaser says, "I know I need a bigger tank. I'll ahve one in the next year or two". Really? I doubt it. And why not wait until you get the bigger tank? Are Nasos not going to be available then?
I know Im micro-critiquing, but its one of my pet peeves. Aquarist should not only plan keeping their livestock for years on teh whole, but also should be prepared for every aspect of the livestock BEFORE they arrive. IMHO.