The definition of SEO is constantly changing. With algorythmic updates bringing new metrics to measure visitor experience, SEO remains static. To be an SEO expert, you will need to be a non-linear thinker. If I were to ask you what half of 13 is, how many answers could you give me? Most only have two: 6 and a half and six and a half. I can think of many more: 6 and a half; thir, teen; 1, 3; one, three; and endless other combinations.
In order to understand Search Engine Optimization, you must be in it for the pure love of the science. I am extremely successful in SEO and I rarely find others who can comprehend the basics, let alone the finer points.