I would love it if Google published an official answer to the perennial client question: "Why can't you get my site to the top of the SERPs for [insert competitive keywords here]?" My answer is usually along these lines: "Your site is competing for placement with many other professionally-built sites. If I'm doing my job properly, and so are the other web developers, none of us is or should be entitled to top placeme…
https://www.google.com/competition/howgooglesearchworks.html
Just to be clear: I recognize that the web developer plays a role in improving Google rankings. I.e. the web dev should definitely follow Google guidelines. But following the guidelines doesn't automatically get you to the top. (What if everyone follows the guidelines? They can't all be in first place.)