SEO is one of the most mysterious areas of Digital Marketing. Most of the digital marketing verticals like paid advertising, email marketing and analytics are straight forward. You can always go back and refer to a document to understand how to do things.
When it comes to SEO, there is a bit of mystery in it. Google doesn’t always tell you why they are ranking certain sites above you and when they change the algorithms. If you want to survive in the SEO game, you need to have good intuition, think like a search engine and use SEO tools to the maximum.