OK we've seen some of our favorites; but what about those shots where the idea was there, but either the timing was just a little off, or the execution was not spot on. The shot maybe looked pretty good on the LCD, but you had to groan when downloaded to the laptop. Try as you might, no Photoshop is going to save it. The shot that you have to go back again to make it work this time.
Well of course I had tons of those and many were way off, but this shot I think failed because the topside part, Sipadan Island taken from Barracuda point, was out of focus. Had my 17-35 with a dioptre on. Went back the next day with the 10-17, and of course the little fishies were impatient and did not hang around for a repeat performance.
Let's see some of yours.
Jeff great thread and I think I know which one is the one for me, but it will also provide for another good story without photo 
On this one I was closing down the camera and heading up, looked backed to the DM who indicated Grouper and I nodded since I saw the big one a little bit off. So swam towards it and started getting strobes positioned. It turned towards me dead on face forward with its mouth wide open wide. And right there was a lobster perfectly positioned - was the perfect amazing shot but I could not get the camera moving quick enough (part of it was holy s4%t am I seeing what I am seeing as visions of the best photo I would ever take flashed through my mind
) and the grouper turned when I was ready though you can see the lobster still. Hung out a bit more but it moved a bit away and never did the full face wide open straight own pose for me again, The other stayed down longer and the grouper and lobster engaged in a battle for awhile, including the grouper spitting it out and bringing it back in.

The second one was another grouper - no photo available. Was at about 40 feet or so towards the later part of a multi-level dive and came a across a grouper under a ledge and this one was posing, no questions asked. Perfect shot. I started to move a bit to tweak the angle and I felt something strange on my left hand. As I looked I watched as my wedding ring slip off and head towards the bottom and it landed 30 feet or so below me just missing a crevice in the rocks that would have taken it away forever. The whole time I watched it head down I was "Please go left and not right." So I did not get the shot and instead headed down following it and grabbed my ring, slipped it on my finger with a sigh of relief and headed up to where the grouper was. When I got back my hand felt strange again and I looked. When I was down getting my ring I had slipped it on my middle finger and when I tried to take it off and move it to the proper finger, it was stuck. One minor curse later and I headed back down back down to 75 feet or so. Slipped it off the middle finger, back on the ring finger and back up. When I told people the story on the boat (including my wife) they all said they were wondering what I was doing, strangest multi-level diving profile they ever saw.