1. Majority of the users use search engines to find their information/resources.
2. These Majority of the users use key phrases to search their required information/resources.
3. Search Engines are built to provide results based on the user searches, which are keyword/key phrases.
4. To serve user searches, Search engines must have the data. But in what format and how? Well search engines reads every website and its pages and index them, search engine crawl each link on a web page and this is how they find other websites which are linked on that particular page(s).
5. Search engines index all such crawled websites then index them categorically based on the content of each page and website as whole.
6. How do search engines know that a particular shoe selling shop is related to shopping category and sells shoes? the answer is based on the content of the page, search engine reads each word on the page diluting the stop words.
7. When an end user searches in a search engine that particular search engine retrieve the website results from its index, the index that is already sorted all the websites based on the relevance category.
This is the main reason for a website owner to do proper keyword research to know what users are search for so that they can come up with best possible keywords which is being searched by users.
For example: Website owner A has a site which sells shoes, they sell to all UK but no international shipping.
If website owner A do not know what users are searching for, they (website owner A) MAY not use proper titles and keywords in their content.
If people are searching for
shoes - searched 900000 times every month (highly competitive keyword, so takes long time to achieve TOP 10 positions)
black shoes - searched 40000 times every month
cheap shoes - searched 60000 times every month
Manchester black shoes - searched 20000 times every month
wedding shoes - searched 10000 times every month
gents shoes - searched 20000 times every month
ladies shoes - searched 25000 times every month
school shoes - searched 2000 times every month
and if Website Owner A uses just "Shoes" as the TITLE of the website
then he will not be able to rank well in the search engines because of the huge competition and majority of the users tend to visit the those websites that are with in TOP 10 search results so it has become very much potential to be on TOP 10 search engine results for the keywords that are being searched every month and that are relevant to your website theme.
So when the owner of site A knows about the keywords that are less competitive but has moderate search count they will use these keywords to rank in TOP 10 in short time frame and attract relevant traffic to the website from search engines.
If you do not know which keywords are being used in search engines by users how can you use those keywords on your title and content in order for search engines to index you in appropriate category and show you for those keywords when searched by the potential buyer/user?
Experience: 10 years
I am in hurry so excuse me for any typos.