Acquiring a raking for a lucrative keyword in the top 5 results in a search engine requires time, energy and effort which is either (a) time you invest or (b) pay others to execute. Much like search engine marketing, you have to know the value of the visitor, what profits you can yield from conversion and whether or not you have the budget, time or energy to compete in that arena.
While it is better to build your website with the SEO ranking objective in mind, this is not always practical; as many business owners learn about SEO after they start their businesses and the website is already built.