Covering an honor with an honor (or not doing so) is perhaps my favorite topic. It's the first "advanced" play I learned. I can still remember where the lady (the mother of a high school chum) was standing when she advised us on this matter. I have no recollection of the first time I heard the word "finesse" in relation to bridge, or most other terms. I believe covering an honor was the first topic I ever wrote on (but not the first published, indeed, not yet published). And not least, I consider it the most under-reported and under-appreciated topic in bridge.
People, I think, regard this topic as infra dig. That's for novices, huh? Well, yes, of course. But it's not just for novices. It's a tricky matter requiring no small measure of acumen to get right. When participating in the discussion group on OKbridge, I submitted the following thought for any comment it might elicit: People are so uptight about sluffs & ruffs that they almost have a heart attack when their partner does allow one even when it doesn't cost a trick. Yet, I would hazard the guess that for every trick lost on a careless sluff and ruff, there are 10 lost through misplays on covering (i.e., covering when they shouldn't, not covering when they should).
The only response I got was a (to me) strange letter detailing what I believe was a failure to split honors, but which in any event had nothing to do with covering an honor. So I'm left to pursue this topic alone, it would seem. But I caution you against treating it lightly or indifferently or beneath your consideration, that is, if you like to win tricks that the cards are prepared to let you win.
First, lemme say that "honor" for this topic alone shall refer to any card that is valuable by virtue of its strength. I don't want to have to say "honor or 9 or 8" every time I use the word. So it might be a nine or an 8 that is at issue, and which I will treat as honors. I even came across one case where a failure to cover a 7 with a 9 cost a trick, though to be sure that was a rarity. Still . .it was there.
Below are links to reasons for covering with illustrations and for not doing so with illustrations.