You might think that the worst thing you can do as a writer is fail to mention something important.
Many textbook authors share this fear, and so cram their paragraphs with every darned thing they can think of in order to make sure no one, and especially not their academic peers, can ever accuse them of failing to mention this or that detail. Conscientious (= paranoid or obsessive) grad students are prone to the same disorder.
But you must not give in to it. For the one thing worse than not mentioning something is mentioning it badly–by which I mean, mentioning it in such a way that the reader doesn’t know what you’re saying.
Historians, for example, must resist the urge to write something like, “The battle was won because of the Spaniards’ technological innovation and strategic superiority”–without telling us what the innovation was and in what the superiority consisted. The problem here is not that what is said is wrong or that it is unimportant: It is that it is opaque. It is a brief patch of fog that stops the reader in her tracks, makes her look around in confusion, and requires her to go back and forth over preceding territory trying to figure out what the heck is meant in this passage.
The “mention” is, therefore, not only a zero, conveying no useful information, but less than zero: actually making the reader’s cognitive situation worse.
To be sure, the industrious reader might be provoked by such a mysterious clue to go to other resources in hopes of figuring out just how the Spanish pulled off that victory. But such efforts must be credited entirely to the reader. The writer cannot congratulate himself on provoking the reader to do extra work by his tantalizing “mention.” The writer is obliged, always, to do the work of a writer: say what you mean so that the reader understands.
So: Say what you mean, fully and lucidly, or drop the whole point. Maybe it’s bad to drop the point, but it’s even worse to keep it but relay it so badly that you actually impede the intellectual progress of your reader.
(Yes, I’ve been editing theses, and I’ve had to write this note on too many of them. So now you know, too.)
(And speakers, yep, the same goes for you, too. Either make the point thoroughly and well, or drop it from your talk, no matter how intriguing or edifying it felt to you when you jotted it into your notes. You, too, will stop your listeners dead in their tracks by the poorly rendered “mention,” and they may or may not get back on track with you after struggling to figure out what you just said.)