Doughnuts and holes

Life can be odd. You hear phrase that resonates -- for example Isabel Swift's mantra of heeping your eye on the donut and not the hole, and suddenly, it seems to keep appearing.
I was rereading Dwight Swain's Techniques of the Selling Writer and he used a variation on the phrase. He used in the context that sometimes writers are so fixated on the exception that they forget the rule. In fiction, every world that the writer creates operates by a certain set of rules. Unless the writer has shown the reader that the world operates by a different set of rules, the reader will assume it operates by a general set of commonsense, societal rule. For example, gravity, or phoning the police when your house is broken into. Or that intense fire burns. But sometimes, you become so focused on the exception that you forget the rule and then the heroine may seem like she is Too Stupid to Live and the reader forgets to suspend disbelief.
If you are going to break a rule, show that it is possible before you break it. This goes back to the whole plotted plant thing.
And it is always a matter of keeping your eye on the doughnut, rather than actually eating it...because the other problem for many writers is the tendency to eat after expending brain power...