SEO is not easy. There are SEO problems all the time that arise if the person doing your website's search engine optimization is not done correctly. Even one little "mistake" by the site's SEO can ruin your entire business. I've seen this too often.
Some of these potential SEO problems can include:
Duplicate Content - people don't want to see the same content over and over again when they're searching for something. The search engines don't want to see it either.
Writing For Search Engines, Not For People - real people are coming to your website. So, you should target real humans, not be writing content that's full of keywords just because you want to "rank well" for a particular keyword.
Poor Keyword Strategy - pair your keywords with the content on your website and the products or services your business offers.
Link Building Issues - links from other websites are "votes" for your website. The more powerful the other website linking to you, the more powerful your website becomes in the eyes of the search engines.
Only utilizing On-Page/Off-Page Tactics - you have to combine both content on your website (on page tactics) with off page tactics to be successful.
Technical Issues - if you have problems with the technical aspects of your website then visitors will have problems, too. If there's a broken link, then search engines and visitors will see those. Fix the technical issues.