Search Engine Optimization is the process of structuring a web page so that it is found, read, and indexed by search engines in the most effective manner possible.
Consider what it would be like if no one could easily find your place of business, or even your telephone number. Most businesses could not continue for long in such a situation.
The same thing can happen with your web site if people cannot easily locate it. Traffic volume, if it existed at all, slows to a crawl. Potentially valuable customers never even know you are there and all of that money you spent on your new website is going to waste.