The two most common reasons for a trademark cancellation are non-use by the registrant and the mark becoming generic. Although a trademark can potentially exist forever, these trademark rights are subject to continued use in commerce. Substantial non-use in commerce provides the opportunity for third parties to file a cancellation before the USPTO. The third party would need to properly detail the grounds for such non-use, and provide specific details that clearly show that you have not been using your mark.
A second ground that can be used to cancel a trademark is that the mark has become generic. This means that your mark has become so associated with the underlying good or service that it is used interchangeably with your mark. Once a registered trademark becomes generic, it is no longer subject to trademark protection- and is thus subject to cancellation. Owners of trademarks, including registered trademarks, should take steps to protect their marks to ensure they do not become generic.
There are other reasons for cancellation, such as fraud in obtaining the registration, which can lead to the cancellation of a trademark at any time. Some registered trademarks, after they have become “incontestable,” are more difficult to cancel. Fraud is one allegation that can be brought at any time; however the standards for proving fraud can be at times difficult.