Probably why you've heard this one before and not the other two.
Plato's Cave is such a good analogy it's extensible. What happens if you drag someone out from the deep cave into the sunlight? They don't learn the truth, their pasty skin gets Plato's sunburn.
If they're used to the cool cave and take off too much clothing in the warm sunlight, they may even be burned fatally. Not to mention they're likely to lose at least some eyesight due to staring into the sun, unless they have a sherpa telling them that staring into the sun is dangerous. Plato's blindness.
Truth isn't safe. (One of my favourite things about it.)
Likewise we can see there's various galleries to Plato's cave. Deeper caves and shallower caves. We can see that the puppets don't dance themselves - someone has to stand in front of the fire and wave them around. They don't necessarily know the truth, but do they know the story is a lie.
"It would be a lot of work to lead his fellows into the light of a kind of new dawn of knowledge."
Not merely a lot of work, but impossible.
Seeming nitpick: truth is far more like darkness than light. Plato was working on a rather fanciful model of vision which was basically [eyes are flashlights]. Visi-ons leave and visiblate objects, which then return the visions to the eye so you can see.
Lies can be major or minor, the way light can be bright or
dim, whereas truth is just truth. There are an infinite variety of
colours of lies, but truth comes in exactly one shade. You get to truth not creating and shining a light, but by destroying all the lies in the way. Truth is what's left once you've laid waste to everything destructible.
In reality, taking a man out of the cave doesn't work. You could say he takes the cave with him, but in fact truth is darkness: he cannot see it. The truer it is, the more invisible it is. You can wave as much truth in front of him as you want to no harm, because he won't even notice. The best you can do is perform a shadow-play that happens to cast the actual shadows on the wall for him to see, but why would he not treat this truth-matched shadow ritual any differently than he treats any other shadow ritual? He doesn't. He can't.
Bonus round: as I found out studying consciousness, nobody has tried Plato's cave-sherpa program. As above, I'm sure it wouldn't work, but nobody really knows. However, lots of folk have tried leading men into even deeper, more crazed, more twisted galleries. Men love that. Huge demand.
To "see" the truth, you have to touch it directly. Why does [Plato's sunburn] work as an analogy? Truth is caustic. It burns. It destroys, violently. Even if you lead a man through the shadows to the darkness, he will recoil in pain. Is it too cold? Too hot? Either way, expect lawsuits. He will blame you for leading him; he will not blame his own weakness. He will cling spastically to his damaged lies, then flee in terror.
Most who leave the cave on their own will likewise recoil, believing they have made a mistake.
He probably isn't even wrong. Fondling the truth too much leads to scarring. What do you do if [too much] means [at all]?