The complexity of Google's Search Algorithm is just like that of a shuffled dealers deck. All the pieces needed to play the game are there, however, input is constant, but output has it chances.
Think of the first page of Google search as a chance for a flush. There are 5108 options (total results). However there are winning hands and losing hands.
SEO is a way to increase your odds of receiving a winning hand. The winning hand is your customers seeing your content or website before your competitors. Simply put, we are trying to work the deck in your favor.
At the very minimum in SEO we are trying to play the game, but get into the game. Not ever card gets drawn in the round, why shouldn't your website be drawn in the first round?
As customers eliminate cards from their hand to create the best hand, that's how our customers think when they search.