As a movie, The Lord of the Rings had quite a few flaws.
The wizard battles had effects worse than martial arts films from the eighties, and the plot developments felt forced, but those were minor issues that could be overlooked.
However, the biggest and most fatal loophole appeared in the final part of The Lord of the Rings—Frodo took the ring to Mount Doom. He climbed Mount Doom and arrived before the passage leading to the heart of the volcano. All Frodo had to do next was walk inside, reach the center of the volcano, and toss The One Ring in. That would have been the end of it.
Yet at that point, an utterly unimaginable problem appeared.
The passage leading to the heart of Mount Doom did not even have a door!
No guards, no gates, nothing! Frodo just swaggered right in!!
When Fang Zheng saw that, he was completely dumbfounded. No matter how he thought about it, he could not understand what Sauron had been thinking. It was not as if Sauron did not know Mount Doom could destroy The One Ring. Logically speaking, such a dangerous place should have been sealed off, even if he did not destroy it.
And Mount Doom was not some remote corner beyond his reach—it was right under his nose!!
Even if the volcano erupted frequently and made it impossible to station guards there, would it have been so hard to send a group of Orcs to block the entrance with rocks? Huh? Was that so difficult?
You were not planning to forge another ring, so why keep the place open? To reminisce about the past?
Could Sauron have gone senile?
Honestly, the moment Fang Zheng saw that, he lost all interest in the movie. It was like working hard to