From time to time I have an idea of setting up a new forum, but I am aware of the potential problems. There are already thousands of forums on a wide variety of topics and it might be hard to compete with more established ones. It is always possible to attract traffic, but that might actually require you to spend some money. Usually that is not an option for a typical forum owner. It might still be a good idea to establish a forum covering some unique topic that nobody created a forum about. This way you would not have to worry about the competition.