I think title of story contains word "suffering".
The word is "sacrifice".
This sci-fi short story was written by a female in the 60s.
It's the 1958 novelette "Unhuman Sacrifice" by Katherine MacLean; first published in Astounding Science Fiction, November 1958, available at the Internet Archive. There is a plot summary at jennre.wordpress.com, which is quoted in the answer to this question.
A missionary persuades a roly-poly young boy to skip a coming of age ritual where the teenagers (all roly-poly and energetic) are hung from gnarled trees with boulders during the beginning of flood season. They all stretch out into skinny low energy adults.
"They are sick because of something they do to themselves. The young ones, strong and healthy, when they are ready to become adults they . . . they are hung upside down. For days, Henderson, maybe for more than a week, the translator would not translate how long. Some of them die. Most of them . . . most of them are stretched, and become long and thin." He stopped, and started again with an effort. "The native boy could not tell me why they do this, or how it started. It has been going on for so long that they cannot remember."
Abruptly, and, to Henderson, shockingly, the preacher dropped to his knees and put his hands together. He tilted his head back with shut eyes and burst into prayer.
"O Lord, I do not know why You waited so long to help them to the true light, but I thank You that You sent me to stop this horrible thing."
The missionary convinces one boy to skip the ritual.
Not exactly. The missionary (Winton) fails to convince anyone, but the engineers take direct action:
"Who is that up ahead with Henderson?"
"Spet, the native boy."
"How did you persuade him to stay away from the ceremony?"
"We found him hanging and cut him down."
"Oh." Winton was silent a moment trying to absorb the fact that the engineers had succeeded in rescuing someone. "It's a different approach. I talked, but they wouldn't listen." He spoke apologetically, hanging onto Charlie's shoulders, his voice jolting and stopping as Charlie tripped over a concealed tuft of grass or small bush under the water. "They didn't even answer—or look at me. When the water got deep they went off in little boats and didn't leave a boat for me."
The boy bends over, grabs his ankles and transforms into one of the gnarled trees.
Spet, the native boy, thinks the Earthmen are spirits or ghosts:
The spirit with the black skin and white face possibly wanted him for his own dark spirit world. He was coming down the ramp at Spet, screaming. He was too late, though, Spet knew that he was safe for the dim land of the drowned with the friendly ghosts who had come for him. He felt his feet sending roots down into the mud, moving and rooting downward, and a wild joy came over him, and he knew that this was the right thing for him, much more right and natural than it would have been to become a tall sad adult.
He had been feeling a need for air, panting and drawing the cold air into his lungs. Just as the clawed hands of the dark spirit caught hold of his neck, Spet had enough air, and he leaned over into the dark and friendly water, away from the painful beauty of the bright lights and moving forms. The water closed around him, and the sound of voices was lost.
He could still feel the grip of the spirit's bony arms around his neck, pulling upward, but he had seen the brown ghosts running toward them, and they would stop it from doing him any harm, so he dismissed the fear from his mind and bent deeper into the dark, and plunged his hands with spread fingers deep into the mud, and gripped his ankles, as if he had always known just how to do this thing. His hands locked and became unable to unfold. They would never unfold again.
He felt the soft surge that was the first flood wave arriving and passing above him and ignored it, and, with a mixture of terror and the certainty of doing right, he opened his mouth and took a deep breath of cold water.
All thought stopped. As the water rushed into his lungs, the rooted sea creature that was the forgotten adult stage of Spet's species began its thoughtless pseudo-plant existence, forgetting everything that had ever happened to it. Its shape changed.