Say you pick some topic you know a lot about. You make a site about it and get many links. You get a certain amount of direct traffic. Will the search engine traffic usually be (a lot?) bigger than the direct traffic you receive?
Usually it seems most webmasters get a lot more traffic from search than from direct traffic, but Im wondering what would happen if one didnt optimize for any keywords or if the keywords were so competitive that one wouldnt get in the top10 for any of the main phrases. Or..or.. would the search traffic usually still exceed the direct link traffic through weird long-tail phrases?
This depends entirely on your site. Sites with loyal members such as forums and blogs tend to get a lot of repeat visitors. Blogs get visitors from blog search engines. There's also social bookmarking sites that can send huge amounts of traffic, and a well-placed link on a high traffic site can send a steady stream of visitors. As for long tail search, popular opinion is that this is a smart goal to aim for.