In my opinion, having a successful forum needs a lot of time, work and probably money. In life, you can't do anything great if you don't love or at least like what you are doing. Creating a forum is easy because of the SMF script, but getting your forum to the "successful forum" state is hard, and maintaining that state is even harder. You need to work a lot, help others and so on. It's not impossible, but neither easy, which makes the satisfaction even sweeter.