For things you can't control, like other players, prediction works fine and can be almost entirely invisible when well done. But prediction doesn't work fine with things you control, like your own character/weapon, because it feels very wrong when you send input and don't get an immediate response.

So for instance imagine you're playing an FPS and if you pressed the fire button, the weapon didn't fire until that packet traveled to the server, was processed, scene rendered, and finally returned. An extra 100ms or whatever might not seem like much, but it nonetheless feels very wrong, and also can have a majorly detrimental effect on skilled players' ability to play the game because you're basically adding that time to their reflex rate. And 100ms is more of an aspirational goal than a typical norm. Stadia, for instance, had latency that could reach upwards of 250ms.