Suppose you have a tool or MacGuffin. It's pretty much all-powerful, and can shoot giant lasers from space! Just one problem... it needs a certain type of ammo. Or some type of battery, in a setting where people are using swords. In any case, the other half of the MacGuffin requires a quest of its own. Worse yet, the "key" part of this equation may be finite, forcing you to keep searching for the object in question (this is particularly the case, in the case of ammo). Compare Dismantled MacGuffin, though this is more about having a tool need to be assembled than having a tool that is worthless without its other part.
- The Green Lantern comic series, has Hal Jordan (and others) spend much of their time heading back to his lantern, because without it, his ring is kind of worthless. (One wonders why he couldn't carry his lantern around in one hand at all times)
- In earlier seasons of Supernatural there was The Colt, a special gun made by Samuel Colt himself, which could kill demons - but you had to have special demon-killing bullets for it and once those were used up, it was just a regular gun.
- In Dungeons & Dragons, if material components is enforced, the wizard can pretty much learn any spells by study, but without components, they can't use most of them. Thankfully, there's usually a Eschew Components feat.
- In the original The Legend of Zelda, you have a few of these, but the most egregious one is the bow in the first dungeon. You need to buy arrows for it to work (in later versions, enemies would typically drop arrows), meaning in all likelihood you'll face the boss with just a bow.
- Also in the Zelda series, bottles are pretty much based around this concept. Once you've acquired one, you still need to find whatever you want to put in it (be it a potion or fairy to make the game easier, or an important item for a puzzle or sidequest).
- Cyborg in Teen Titans normally has his power work without a hitch, but in two occasions, it is shown how fragile his power base actually is. The first is when Starfire visits the future, and his systems actually went obsolete. The second is another episode where he gets stuck in an alternate history that has ancient technology and he can't power his suit.
Hello, Unknown Troper. You'll need to get known to lend a hand here.