You think you run a tight ship. You think, "Sure there's room for improvement and perhaps I could mop the floors more often, but on the whole, in the cleanliness stakes, and especially as I do it all myself thanks to the GFC, I give myself an honest 8 out of 10". You assume 8/10 is good enough. And then you look behind the big TV unit thingee looking for the lost library books. And you see the evidence.
And you know then, in a heartbeat, that 8/10 isn't good enough.