While having your main keyword in your domain name may help your site getting ranked for that particular keyword, it is not the only or most important factor to search engine optimization. High quality SEO involves several other techniques besides just optimizing your domain name. Besides you most likely want to rank for dozens of different main keyword phrases, so if your domain is your only strategy you will be greatly disappointed.
Don't get me wrong here, I'm not saying that having a specific keyword in the name of your domain won't help, I'm just saying that if this is going to be your main strategy to getting high search engine rankings then you need to rethink your SEO strategy. When I first started focusing on optimization techniques or my websites about 7 years ago, I use to think that the domain name was the most heavily weighted factor in the search algorithm of the major SE's.
Having a main keyword in your domain did actually use to be more important, but as time has progressed this factor has become less important. Think about it, some of the most popular and authoritative websites online rank number one for keywords and phrases that are not in their domain name. Amazon.com and Ebay.com just to name a couple, rank #1 for hundreds or actually even thousands of different keywords and key-phrases that are not in their name! How can this be?
Well, this is because having an important keyword in your domain name is not the most important factor to getting top position! Link popularity and longevity of a domain are two of the most important things in determining rankings. Of course the content or information on your website is a key factor also. It is the combination of many different things that help the search engines decide how your site will appear in their results.
So remember, there is more to getting #1 rankings other than a keyword rich domain name. With all this being said, having a keyword that you want to rank for in your domain will still help, but if this is your main SEO strategy, then you probably will not be successful in getting the results that you desire. Achieving the first page of Google, Yahoo, or Bing requires a lot of time and effort. Just make sure that you take that into consideration when starting your website.