It might be the most devastating scene in The Return of the King
Frodo isn't weak here. He carried the Ring farther than anyone in Middle-earth could have, and it's eaten through him. He can't even remember the Shire anymore. He left to save home, and the Ring took the memory of it, so he's still crawling toward a place he can no longer picture
Then Sam does what Sam always does. No speech about destiny. He knows there's one thing he can't lift off Frodo's shoulders, and he doesn't pretend otherwise. "I can't carry it for you, but I can carry you."
That's why Sam is the heart of the trilogy. He isn't powerful like Gandalf or a king like Aragorn. His virtue is smaller and much rarer. He just won't leave
Tolkien said Sam came from the soldiers he served with in the First World War, men he thought were braver than himself. It shows. Sam was never the chosen one. He's the friend who keeps walking when the weight has stopped being anyone's to carry alone
Frodo was the hero the world needed. Sam was the hero Frodo needed. Sometimes you can't lift what someone carries. You can lift them