general What example do you know of "Cool idea, but not a good/practical idea"?

[Slappy Bird 118]

Basically, anything that looks and sounds cool on paper, but is impractical because of circumstance and drawbacks that make not as useful as you may think. Could be in real life or fictional (I'll be expecting a lot of video games example for the latter)

I'll start:

- Any sport cars (they're fast, and basically a status symbol, but most only allows 2 people inside, very expensive, and will raise your insurance rates)

- One-time pads encryption (literally unbreakable message without the key, but the key must be long as the message, the encryption key for it may never be reused for encryption again, and if you lost the key: the message is gone forever)