If only it were this simple with every case. What if you applied for a trademark sometime ago, but haven't released your product yet and someone comes along and

If only it were this simple with every case. What if you applied for a trademark sometime ago, but haven't released your product yet and someone comes along and releases a product with your trademark (unintentional of course)and becomes fairly successful ? I am not debating the article. Just wondering what would be the most ethical thing to do.