For instance, did you know when blog owners lose traffic to Google updates, they have no idea what keywords or pages were making them money in the first place? They have no idea it may have only been a handful of keywords that were actually making them money.
Once a Google update hits, they go into panic mode and hurry to make their site better. And sadly it takes time and many never get back the traffic they once had.
They never understood that they could have bought some traffic while work on their site post algorithm change to keep the traffic rolling.
And not to mention they should have been building an email list all along which is the ultimate form of blog marketing.