I believe that the article is correct. The keywords is not the only thing search engines see in a site for rankings. But your theme is very broad. So you can write about Finance and self improvement and anything that makes your life happy. So it should be fine.

I am trying to decide if my site concept is too broad. My theme consists of health, wealth and happiness; an overall success plan. This is what I would love to talk about. I don’t want to feel limited. One company says as long as my key words relate to my product it won’t affect my ranking with google but I just read an article that says search engines don’t just look at key words they look at overall theme of your site which can affect your ranking. If this is true how do I know if these concepts are related enough? Please help.