The more a company's positioning rests on activity systems with second- and third-order fit, the more sustainable its advantage will be. Such systems, by their very nature, are usually difficult to untangle from outside the company and therefore hard to imitate. And even if rivals can identify the relevant interconnections, they will have difficulty replicating them. Achieving fit is difficult because it requires the integration of decisions and actions across many independent subunits. A competitor seeking to match an activity sys- tern gains little by imitating only some activities and not matching the whole. Performance does not improve, it can decline. Recall Continental Lite’s disastrous attempt to imitate Southwest, Finally, fit among a company's activities creates pressures and incentives to improve operational effectiveness, which makes imitation even harder. Fit means that poor performance in one activity will degrade the performance in others, so that weaknesses arc exposed and more prone to get attention.