If you want to keep your sites up and ranked high them you need to learn theme density.
SEO is only working with keywords whereas
Theme Density works with the structure of your website and its content.
Its the same scenario as if you wanted to build a house. You may have nice location and great neighborhood, but what about the foundation and structure of your house will it last a long time. Is it structured to withstand major weather problems or terminite infestation (Googles slap)?. What about the furnitures and appliances (the content), are they suitable to live in with?.
I can tell you 99% of webmasters today don't know what a few of us know. I'm not trying to be arrogant or anything. It's the fact and the fact is in Theme Density is Master.