Just noticed my coffee mug lid has text saying "See important warning on bottom of mug". Why it's not "bottom of the mug"? It is very specific mug this lid connected to, this is why I expect it to be "the mug". From other side if it is any other mug the lid fits it should be "a mug", shouldn't it?
How in this case I understand "the" or "a" is not needed?