Some races tried to expand too fast, held poorly organized events, and went under. The bigger races became crowded, studded with long lines, and covered in corporate sponsorships and commercialization. Some courses were watered down both in number of obstacles and in their caliber in order to attract a broader swath of possible participants; obstacle course organizers are truly faced with a dilemma — how to make their courses tough enough that it feels like a challenging experience, without chasing away too many potential customers. This tension is reflected in many OCRs low retention rates; for example, only 20% of those who do a Tough Mudder end up doing another. Once the novelty is gone, a sense of been-there-done-that sets in, leaving people with less will and motivation to participate again in something both expensive and physically strenuous.