Just like you shouldn’t rely on a single source of income lasting forever, it doesn’t make much sense to concentrate all your resources in just one marketing arena. 
Why not? Because things change! Consumers are always changing their habits and the “next great thing” fall in and out of fashion quickly. If you concentrate just in one area and the marketing wind changes direction – you could be left holding a basket of nothing (or, 10,000 unwanted direct mail pieces)! This blog post (by @mattmcgee) succinctly points out the folly of picking just one marketing arena http://www.smallbusinesssem.com/do-not-follow-this-social-media-advice/4030/