Humans can think inhuman thoughts.

Learnin’ how not to do things is as hard as learning how to do them.

Humans! They lived in a world where the grass continued to be green and the sun rose every day and flowers regularly turned into fruit, and what impressed them? Weeping statues. And wine made out of water! A mere quantum-mechanistic tunnel effect, that'd happen anyway if you were prepared to wait zillions of years. As if the turning of sunlight into wine, by means of vines and grapes and time and enzymes, wasn't a thousand times more impressive and happened all the time.

Ye ken, we've been robbin' and running aroound on all kinds o' worlds for a lang time, and I'll tell ye this: The universe is a lot more comp-li-cated than it looks from the ooutside.

He found that he had this sudden desperate longing for the fuming, smoky streets of Ankh-Morpork, which was always at its best in the spring, when the gummy sheen on the turbid waters of the Ankh River had a special iridescence and the eaves were full of birdsong, or at least birds coughing rhythmically

It must be hard for humans, forever floundering through inconvenient geography. Humans are always lost. It's a basic characteristic. It explains a lot about them.

It is possible to live well with dementia and write best-sellers 'like wot I do.