The examining attorney denies and refuses the application for your trademark if at all your trademark closely resembles any other existing one. Imagine, there is another application submitted for approval at the same time that you sought for registration, and both are designed similarly!! Obviously, priority will do there. The one that is submitted first is likely to get registration.

You will be notified that there is another application pending that has a trademark that is similar to your own. If that similar trademark will be denied for some other reasons, then you will be liable to get your trademark registered. The conflict is when that trademark gets through and acquires the status of being registered. Then your trademark would not be filed with the federal process. It is the examining attorney who makes the decision regarding the issuing of how similar two trademarks can be. If there is similarity, the secondly filed trademark will be rejected.

This will be particularly difficult provided you have spent dollars and hours working on developing the right trademark for your specific business or product.