1) seeing the SR71 fly numerous times, and never managing to take a single photo of it in the air, taking off, or landing.
2) spending what felt like days sometimes being dragged as a kid during school holidays, to sit by a fence at Mildenhall, Lakenheath, Wattisham, Woodbridge, Bentwaters and not really appreciating it, so even though I got to see lots of cool stuff flying, at the time it seemed quite boring
3) so not taking any photos of all this cool stuff flying either because it was just always stuff that was there every time we went.
4) going to lots of airshows in the mid 80s, ending up with photos of small grey dots in grey skies. or just left the camera at home, so even the crazy unique stuff are now fading memories.
5) taking Concorde totally for granted, my parents even did one of those trips to the bay of biscay on it once as a wedding anniversary gift, and we didnt even take a photo of it taking off.
6) taking Mildenhall airshow for granted, stopped going in the mid90's kept thinking Id go again the next year, but the next year never came