Stage 2: Dirt Ignorance. This is when the dirt is visible but you have entered into a peace treaty with it. So long as it does not wave its hands in the air, embarrass you with horrible smells or cause botulism or other fatal illnesses you are willing, in return, to ignore it for a little while longer. From this state it is possible to progress to Stage 4.
Stage 3: Dirt Flabbergastedness. This is when the dirt blindsides you into such a state of shock, that you cannot possibly ignore it. Like when you look over your husband's shoulder while he is hugging you and blurt out "My god! When did the ceiling fan get that disgusting?!?!" and you push him away and immediately climb on the table, shouting for Clorox, rubber gloves, a tarp, copious amounts of hot water and possibly the National Guard. Note the difference from Stage 2. From this stage you skip right over Stage 4. There is no progression except into disgust with everything followed by exhaustion and possibly death (sometimes your own, but not necessarily).
Stage 4: Dirt Eradication. This is when all dirt is banished from your home at the same time. A very rare condition that if you are lucky enough or insane enough to reach, it will be fleeting. How fleeting depends on how many people share your house and how adept they are at picking up after themselves. In other words, about five minutes. From this stage it is possible to continue back to any of the previous stages, either exclusively or in progression.