Not luck. Malicious computer spirits. With a bad sense of humour.
I usually don't bother with the "reload and try again" trick when opening loot chests, since - if I do use it - I invariably beat a disproportionate amount of hours to death with it while trying to maximize. It is not good for me.
However, yesterday, while cleaning out Stone's Flying Fortress, I found not one but
two golden chests standing only meters apart in the same court yard. And I have been looking for a level 9 melee damage protection formula for some time now. Once I got that, I could relax the whole loot routine. It was too good an opportunity to pass up.
After two hours of reloading and chest-opening, I had located at least five or six level 9 ranged or magic protection formulas, both of which I already own. On top of that, and this is the part that ticked me off, I had found two level 10 melee damage protection formulas - which I seriously don't want, because I'll never use up a malachite gem on defense.
Now I know that there really aren't any kind of malicious computer spirits. They ain't real.
But if they were, they would be having a ball.