Google claims their users click (organic) search results more often than ads, essentially rebutting the research cited above. A 2012 Google study found that 81% of ad impressions and 66% of ad clicks happen when there is no associated organic search result on the first page. Research has shown that searchers may have a bias against ads, unless the ads are relevant to the searcher's need or intent 
The thing about SEO in 2018 is that Google changes its algorithms more than once a day! Reports say that the company changes its algorithms up to 600 times a year. While the majority of those updates consist of smaller changes, among them is the occasional, major update like Hummingbird or Panda that can really wreak havoc with your traffic and search rankings.
Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag or index files in engines like ALIWEB. Meta tags provide a guide to each page's content. Using metadata to index pages was found to be less than reliable, however, because the webmaster's choice of keywords in the meta tag could potentially be an inaccurate representation of the site's actual content. Inaccurate, incomplete, and inconsistent data in meta tags could and did cause pages to rank for irrelevant searches.[dubious – discuss] Web content providers also manipulated some attributes within the HTML source of a page in an attempt to rank well in search engines. By 1997, search engine designers recognized that webmasters were making efforts to rank well in their search engine, and that some webmasters were even manipulating their rankings in search results by stuffing pages with excessive or irrelevant keywords. Early search engines, such as Altavista and Infoseek, adjusted their algorithms to prevent webmasters from manipulating rankings.
This refers to your ability to rank for certain keywords. For instance, say you sell shoes online, you will need to optimize your site, backlinks, website speed and much more so that you can “rank” high for certain keywords that are highly relevant to your business. Relevant keywords may include “buy shoes,” “shoe sale,” “where to buy shoes,” and so on. Once you can rank high (top page) for these keywords, you will enjoy an increase in traffic and business as a result.
In December 2009, Google announced it would be using the web search history of all its users in order to populate search results. On June 8, 2010 a new web indexing system called Google Caffeine was announced. Designed to allow users to find news results, forum posts and other content much sooner after publishing than before, Google caffeine was a change to the way Google updated its index in order to make things show up quicker on Google than before. According to Carrie Grimes, the software engineer who announced Caffeine for Google, "Caffeine provides 50 percent fresher results for web searches than our last index..." Google Instant, real-time-search, was introduced in late 2010 in an attempt to make search results more timely and relevant. Historically site administrators have spent months or even years optimizing a website to increase search rankings. With the growth in popularity of social media sites and blogs the leading engines made changes to their algorithms to allow fresh content to rank quickly within the search results.
PPC gives you the ability to fix your daily budget depending on how much you’re willing to spend. And since you can start off with a small amount, you don’t have to put a heavy investment at stake before testing the waters. Once you know a certain campaign is giving you a good return on investment, you can ramp up your budget and increase your ad spendings without worrying about incurring losses.
Organic search should not be viewed as just one of many different marketing strategies. Instead, it should be the cornerstone of your efforts. Your materials should all be optimized to maximize their appearance on the SERPs. You should also be using the insights that can be gleaned from organic search to inform the rest of your marketing endeavors.
At our agency, we work with sites of varying sizes, from very large to quite small, and recently, we have noticed a trend at the enterprise level. These sites aren’t relying as much on Google for traffic any more. Not only are they not relying on Google traffic, but also, the sites are getting less than 10 percent (or slightly more) of their organic traffic from the search giant.