The injunction that artists and writers should "know the rules before breaking them" is perfectly sound if it means that they should make the effort to acquaint themselves with the history of the artistic form they are using. But if it it means that, in addition to understanding the context within which that form has developed and is now intelligible at all, the artist should have to produce works following the rules before venturing beyond them, this admonition makes less sense.
No doubt student composers or painters sometimes do a kind of apprentice work mastering certain "basics" or emulating works of the past as a way of initially situating their own later work in traditional practices, however much they may eventually depart from those practices. Probably many young writers being by doing something similar, but now creative writing programs so reflexively reinforce rules and conventions already that it's hardly the case student writers need to more intensively imitate established methods. The author of this blog post seems to suggest it's not so much that apprentice writers need to learn how it's always been done as that already published writers need to hold up and show more respect for the tried and the true. This of course amounts not to permission to disobey rules when you know how to break them, but insistence that you just obey rules.
In my view, almost all discussions of "craft" or shopworn advice about how to implement this or that customary strategy implicitly reinscribe the rules successful writers ought to obey. The result is much fiction that competently, if dispensably, applies conventional wisdom, and little that challenges this wisdom or attempts to revise the rules. Writers should absolutely be as well-read and as well aware of how the possibilities of the form (fiction or poetry) have been perceived by writers in the past as they can, but that they should be discouraged from seeing other possibilities, from believing that some of those earlier ones have played themselves out, does not follow.
Ultimately no writer can completely break the rules because the result would be literally incomprehensible. Something so thoroughly new that it can't at all be recognized as participating in the tradition that initiated and shaped the form is indeed a new form and must be judged by criteria appropriate to it. Sometimes,it seems to me, readers and critics are so anxious that the pleasures they associate with a literary form be preserved that more adventurous, rule-disregarding work becomes a threat. Such an attitude is itself what threatens the endurance of a literary form and its pleasures, since only the adventurous writing renews it, prevents it from becoming so convention-ridden the pleasures merely become rote.