More than 80% of all US net users have consulted a search engine, and 29% of people turn to search engines every day to find information online.
-Pew Internet project survey   Read in BBC

This is similar in other countries also. But what do these net users find in response to their search? More than 1,000,000 results? And where do your website stand - no. 1 or no. 1000 in the sequence of search results? If you want your website to have visitors, you need to constantly ensure that you are at the top end of the results list.

More than half of users checked out only one result and more than 80% stopped after looking at three results.
-Dr Jansen and his co-author Professor Amanda Spink, who have analysed more than 450,000 web queries submitted to the AlltheWeb.com search engine in a 24-hour period   Read in BBC

So why do I need SEO expert?

Go through this posting in a forum. The webmaster was confused why his website was not coming in the 1st page for a keyphrase. And here's the posting after he got satisfied on following the expert's advice.

SEO -An Ongoing Process

Today you are among the top 10, and tomorrow you are nowhere in top 100 on the results list.
Reason:

• Regular changing of search engine algorithms.
• Increasing of competitors.

Isn't banner advertisement a better way?.

Online shoppers are nearly three times more likely to find what they want on the Web by using search engines versus responding to advertisements.
-Internet financial transaction firm WorldPay based on responses from 15,235 online shoppers in 124 countries.  ..Read in detail..

Benefits of Search engine optimisation:

• The most economic way to find potential customers.
• Most effective way to target potential customers.
• A marketing form that is accessible 24 X 7.
• Assurance that you will get full value for your website investment now and in the future.

Related articles:
Ten Tips to improve Search Engine ranking
Search Engine Submission Guide