The Reality Stone could accomplish far too many things, but making it produce whatever effect one wished on its own was hardly possible.
For Malekith to use it to plunge the entire universe back into darkness, several factors had been crucial.
First, a lightless environment had once truly existed as a cosmic ecosystem. As long as there was data, there was no need to imagine its details from nothing.
The Dark Elves had been born in that era and lived for a long time. The device they left behind had been created by gathering all the wisdom of their race at the height of its prosperity. To them, using the Reality Stone meant restoring an ecosystem, not creating a future.
Even the technology Divan had provided Thanos had a basis to follow: since Jump Points and Hyperspace Lanes existed in the universe, there had to be a process behind their formation that could be studied.
Though Divan appeared frail, he was an immortal nearly as old as the universe itself. It was hardly strange that he had recorded that process.
Both technologies used the Reality Stone to replicate natural laws. Nature itself was what they imitated, and ancient devices recorded every miraculous stroke of nature's craftsmanship.
Actively compressing a Blue Giant and controlling its volume and mass within a safe range was different. That was artificial interference with natural laws, and many of its details had no model to reference.
In other words, Harry had to learn to become a natural law, to make his will into a law.
And to use imagination to drive this Stone, he needed an immensely powerful will.
"So, we need to remove the Stones from the Scepter and set all three Stones into a single device."
Eitri explained his ideas. Much of the information