Major spoilers for Dune, Dune Messiah, and Children of Dune.

The series starts with the gom jabbar, a painful test of humanity. Humans will suffer for a cause: animals have no concept of the future, but humans will endure pain for a future benefit. Gaius Helen Mohiam's example is an animal caught in a trap chewing off its limb to escape; a human would stay in the trap to kill the trapper and protect their kith.

In Dune, Duke Leto is human. When caught in a trap (Yueh), he attempts to kill his trapper (Baron Harkonnen).

The Baron is the least human: he indulges in pleasure to an unhealthy degree, refusing to suffer for even his own future good.

The Fremen are the most human. They bear the pain of Arrakis for the future reward of Paradise.

In Dune Messiah, the tragedy of Paul's victory is that he made the Fremen less human. No suffering, no humanity.

In Children of Dune, Leto II sees the future and the necessity of the Golden Path: humanity must stop suffering for so long that they learn for all time that suffering is essential to humanity. Leto is more human than Paul, as he's willing to walk the Golden Path, suffering for a future benefit. Ironically, this requires that he reduce suffering and become less human himself.

I predict that the end of the Golden Path will be reached at the end of God Emperor of Dune. Leto will give humanity a goal that they must suffer to accomplish, restoring humanity to the Fremen and elevating the other subjects of the empire.