I already game-mastered 4.5 sessions of Numenera.
An issue I constantly ran into was: how much of the numenera can be understood, especially by a specialized nano with 2 assets (meaning: the most knowledgeable character possible)?
One demonstrative example from an adventure I found is:
You enter a large cavern. The walls are made of unnaturally smooth stone or synth. In the center of the room stands a large ring of the same metal, 2 meters in diameter. A thin membrane vibrates inside it under seemingly strong tension but without actually touching the ring. As you draw closer, you notice the air, the ground, even the walls vibrating, humming in unison with the device.
My intention, coming from D&D and new to Numenera, would have been: Disturbing the device intensified the humming, breaking the membrane makes insect-like beings emerge from the ring like from a portal. Or turning the device towards a crack in the wall widens the crack so they can pass through. Something that would just be a magic portal in D&D.
I always want to treat 'understanding the numenera' like 'investigating what it does': The PC can find out that the vibrations only go in one direction, that the device can be turned, that there seems to be something behind the membrane that causes the humming, etc.
What my players want is 'why is this here, what is it for, what is it made of, can I take the source of power, how can there be something behind it, can I understand the portal technology, can I take the vibrating element from it and attach it do my weapon'.
They want to treat numenera like cars and nanos as physics professor/car mechanics. They think that they should be able to understand what cogs are for what purpose and how to break or alter the mechanism.
For me, Numenera is even more magic than D&D magic. In D&D, wizards can understand what a curse might be placed for, to keep someone out or something in, to make sure only the worthy can enter etc. In Numenera, even this is an unknowable factor.
But what is the understanding skill good for then? Understanding Man-made contraptions from salvaged numenera? Just identifying bits to use as ciphers?