Unlike that magical, mythical baseball field in Iowa - if you build your website - there is no assurance that 'they' will come. Even if you know who 'they' are and you have designed your website to meet their wants and needs - your website can go undiscovered on the internet.
Being found on the internet today almost always involves Search Engine Marketing of some description. Whether it is for Organic ('natural' Search Engine results) and/or Sponsored (paid Search Engines ads), most websites today need to make substantial efforts to be noticed by the major Search Engines.