Have you ever "invented" something in your mind that later became a real invention from someone else?

When I was 17 (1992) I had an idea for a new cartridge for the "1911" pistol platform. I wanted it to be .50 caliber, and I figured that if it were the ~same overall length as the .45 ACP cartridge, and used a "rebated rim" that was the ~same diameter as the .45 ACP's "rim," then it could work in a 1911 as-is, only needing a different barrel and magazine. I estimated that with a 300-grain bullet, you could get around 700 FPS without exceeding the relatively low pressure that you get with a standard 230-grain .45 ACP cartridge. I thought the ideal name for it would be ".50 ACP," though that couldn't happen unless Colt was onboard ("ACP" stands for "Automatic Colt Pistol").

I was working on the weekends at a laundromat at the time, and there was an older guy who always came in to do his laundry and talk guns. I told him about my idea and he argued that a .50 caliber cartridge could never fit in a 1911 as-is, i.e., he claimed that the frame and slide would need to be wider. I disagreed.

In the early 2000s when I first got a PC and internet access, I made a thread about my idea on the Guns & Ammo forum, and I encountered the exact same naysayer arguments as I got from the old guy in 1992.

Then in 2004 this came along...

https://en.wikipedia.org/wiki/.50_GI

... exactly as I "invented" it in my mind a dozen years prior (except for the "GI" name). Even the ballistics were exactly as I predicted (300 grain bullet @ 700 FPS), and it works in a standard size 1911 platform. It never became much of a success, but it did allow me to go back to that Guns & Ammo thread that I'd made a couple/few years earlier and say, "I told you so."