A plateau, geographically speaking, is defined as an area of relatively level high ground. The South Rim of the Grand Canyon, for example, is part of the Colorado Plateau, at an average altitude of about 7000 feet above sea level.
Plateau can also be defined as a state of little or no change following a period of activity or progress. “Progress” is a relative term, but it seems possible that a person could “plateau” in terms of their beliefs about any number of things. Perhaps doubt creeps in. Or one somehow just comes to know all one needs to know. It’s this sort of plateau from which a person is tempted to lob all manner of ill-informed, narrow-minded sludge and venom.
The view from the South Rim is expansive and breathtaking. I’ve never been to the North Rim. I see, though, that on average it is about 1000 feet higher.
It would be good to check that out some day.