Why Do Many Powerful Items Appear Only Once and Then Disappear?

Ha, that's hitting the nail on the head! When I watched Doraemon as a kid, I always wondered too: why didn't Nobita use an overpowered gadget like the "What-If Phone Booth" to solve all his problems? Growing up and rewatching it many times, plus learning about storytelling, I gradually figured it out. There are actually quite a few reasons, let me break it down for you.

1. For the "Story" Itself: Plot Necessity Comes First

This is the core, fundamental reason.

Think about it: each episode of Doraemon is a standalone short story (excluding the long adventures). Its basic pattern is: Nobita encounters trouble → Cries to Doraemon → Doraemon pulls out a gadget → Nobita solves the problem but gets cocky and messes up → Learns a lesson in the end.

The core of this pattern is the "story" and the "lesson." The gadget is just a catalyst, a "key" to drive the plot forward.

One-Time Gadget, One-Time Story: Many powerful gadgets, like the "What-If Phone Booth," the "Dictator Button," or "Liar 800," have effects so strong they can fundamentally alter the world. If such gadgets appeared repeatedly, the story couldn't be told. For example, if Nobita used the "What-If Phone Booth" before every exam to wish for "a world where I always get 100%," what meaning would effort and growth have? The story's fun would vanish. So, these gadgets exist for that specific, impactful episode. Once the story is told, their purpose is fulfilled.
"Convenient Tool" vs. "Universal Key": If Doraemon's pocket always contained a few invincible gadgets, Nobita's optimal solution to any problem would always be one of those. Then, we wouldn't see the diverse, imaginative new gadgets, and every episode would become boring. The treasure of this work is the imagination of author Fujiko F. Fujio. He wanted to showcase a world of infinite possibilities, not one solved by a few bug-level gadgets.

2. Avoiding "Game Balance Breaks": Maintaining Story Balance

This is easy to understand using gaming concepts.

In a game, if a player gets a +9999 god-tier weapon right at the start, fighting any minor enemy or doing any quest becomes pointless. The game's "balance breaks," losing all challenge and fun.

The world of Doraemon is the same.

Powerful Gadgets = Broken Balance: Gadgets like the "Dictator Button," which makes anyone you dislike disappear, go beyond solving problems; they destroy the story's basic setting (like relationships, social rules). If Nobita could use it anytime, Gian and Suneo would have vanished ages ago, and the story couldn't continue.
Preserving the "Weak" Nobita: The story's foundation is the growth of the "loser" Nobita. He must be the kid who's bad at sports, bad at studying, and always getting bullied. That's why Doraemon's presence makes sense, and his growth and occasional moments of brilliance feel precious. If he had a bunch of powerful gadgets, he wouldn't be the Nobita we relate to and sympathize with anymore. The story's foundation crumbles.

Therefore, those overly powerful gadgets must be "one-time use," like a "plot weapon" in a game that can only be used in a specific level. Once used, it's taken away to ensure the game can keep going.

3. Some "In-Universe" Explanations: Doraemon Isn't Omnipotent Either

While there's no official compendium explaining every gadget's fate, we can find some plausible "excuses" in the story's details:

They're Rented: Some gadgets, especially expensive or special-function ones, Doraemon can't afford to buy. He "rents" them from the Future Department Store and has to return them after use.
They're Single-Use: Like many things we buy now, some gadgets are consumables, used once and gone.
Broken or Lost: This is super common! Nobita is a "disaster magnet." Breaking or losing gadgets is routine. Many useful gadgets probably ended up permanently wrecked after one of his mishaps.
Confiscated by Doraemon: For gadgets deemed too dangerous (like the ones mentioned above), after one harrowing experience, Doraemon surely thinks, "This thing is too dangerous, can't let Nobita use it again," and locks it away or sends it back to the future.

These explanations make the Doraemon world richer and make the "one-time gadget" phenomenon seem more reasonable.

4. Maintaining Freshness: A Constant Stream of Imagination

Finally, looking at it from the creator's perspective.

Fujiko F. Fujio's imagination was truly boundless. It's estimated he created over 2000 gadgets. For him, constantly conceiving new, interesting, and varied gadgets was far more creatively exciting than reusing old ones.

Each time something new is pulled from the 4D pocket, it's a surprise for the reader. This "lucky dip" anticipation is part of the charm that has kept Doraemon popular for decades. If it were always the same few gadgets, the charm would fade.

To Sum Up

Simply put, those powerful gadgets are like "plot-limited editions." They exist to:

Serve a specific, impactful story.
Prevent the protagonist from becoming invincible, thus preserving story balance and fun.
Give the author a chance to showcase an endless stream of imagination.

It's precisely because they appear only once that these stories and gadgets leave such a deep impression on us. That's why we still talk about the "What-If Phone Booth" and shudder at the "Dictator Button." This "rarity" is what makes them classics.