It's funny that we use terms like "expert" to describe an SEO. When looking for someone to help us get us top search engine rankings, we often look to see who the experts are. Last time I checked, we don't look for "expert lawyers" or "expert doctors" or "expert plumbers". No, we look for professionals.
However, we do often look for experts at certain subsets. Such as lawyers that are divorce experts, doctors that are cancer experts, plumbers that are… um, clog experts, and so on. So why do we look for SEO experts? Can anyone truly be an expert in all things related to SEO?
Perhaps. Just like doctors can be experts in multiple areas, lawyers can be experts in multiple fields of law, and plumbers can be experts in multiple types of… um, clogs, SEOs can be experts in several areas as well. But an expert in all of them? Hmmmm, not likely.