For example, you have might have a website where all you want to rank for is your brand name or your actual name. This might be of interest if your a lawyer or real estate agent. Another cause may be is ranking for a number of keywords related to your service or product. And finally, we have an online store where each and every product you have has to be optimized and ranked. As you can see there are a number of factors even before we get to the actual SEO or competition or current state of your website.
SEO requires a lot of research and having the right expert can make all the difference in the long run. As along with that research large scale planning is required of site architecture and structure. Making sure the right URLs have been made into canonical all require experience and knowledge.