Breaking up is hard to do, but pouring your heart out on paper is rather awkward. There is really no need for any other information in your resignation letter (including a reason __ which is completely optional). No effusive template and formatting effort is required. This is not a letter that is going to be hanging on anyone's wall, and it probably won't even be filed away!
Spot the Signs. Again, you may receive this response if you have specialized knowledge that would make it difficult or time_consuming to hire your replacement__or if it would be helpful for you to be actively involved in that search.