Sorry, I should explain. The Zodiac Spear is the best weapon in FFXII, with unmatched attack power. The simplest way to get it is avoid opening four other chests scattered across the game (with no hint to this effect anywhere in-game) and it'll be in a chest. The only other way to get one is to open a different chest with a 1/1000 drop rate. Next to the Bazaar, the treasure chest system is the worst-designed aspect of FFXII.

Nothing to do with FFT, just to illustrate how ridiculously long the odds of getting some rare items are in other games.