Natural search engine rankings are vulnerable because of the way Google handles search engine results pages (known as SERPs).
Mike Murray, Proximity Marketing’s senior SEO strategist, details the issue and outlines key strategies in a new Content Marketing Institute article: SEO Marketing Strategy: Tips for Success in 2018
• Track your search engine rankings
• Don’t view SEO as a one-time practice (always tweak pages)
• Analyze ranking and website traffic data to determine when it makes sense to create new content
• Focus on keywords that your website can reasonably target (i.e. respect the competition but understand and leverage your SEO and content strengths)
At the end of the day, there are many moving parts. But your natural rankings may be pushed down as Google works in other elements that essentially push down rankings. In effect, your #1 ranking may be a #5 because Google showcases everything from a series of related search queries to a pack of images before many of the regular results.