Though SEO may seem like a brainless solution and an easily implemented strategy, it is actually not a ‘one size fits all’ strategy or solution. To assume that SEO can be implemented at all organizations and within all digital marketing strategies is similar to assuming that Twitter is the best way for ALL organizations to reach their customers, even a company that targets a demographic who does not use twitter.
The way that SEO fits into your marketing strategy is almost entirely dependent on what it is you are looking for as far as the purpose and objectives of your site and ads. For example, if you have tangible and quantified goals and a campaign such as a sale or promotion, perhaps paid advertising is a better strategy than SEO as it is more of a guarantee and a shorter term solution that is both easy and (can be) affordable.
If you are looking to gain a significant marketshare and long term relevance, SEO is a great way to do so. If you are looking for sales, increased interaction, and impressions, in other words prominence, then paid advertising can be more helpful than SEO.
SEO is also timely and requires significant work, not to say that other forms of digital advertising do not, but there are guidelines and standards that a website must meet to find itself in the top results of search engines like Google, Bing or YouTube. This means that even if you make sure that you have the right keywords, quality content and appealing visuals, that if you do not mean the guidelines, you may be out of luck in terms of appearing in that top spot on google.
SEO comes with no guarantees. Though algorithms and formal calculations help you in appearing in organic search results, there is no payment for coming on top, so there is still an element of uncertainty. Algorithms change frequently meaning SEO needs to be monitored.