There are many potential obstacles for a trademark application. In my experience, the biggest obstacles are:
- a proper description of goods or services
- submitting proper evidence of use
- a failure to properly search for conflicts before applying
- a likelihood of confusion with a registered mark; and
- the overall complexity of the process and its procedures and deadlines.
For more Peltonisms, see: https://www.erikpelton.com/resources/peltonisms/