This isn't Sun Wukong's first journey to the West.
He's lived through it once before.
In his previous life, he really was imprisoned for five hundred years, made to wear the Golden Hoop, tasked with escorting the scriptures, and hailed as the Victorious Fighting Buddha. Then he discovered it had all been a lie.
After attaining Buddhahood, he lost all his memories and became a lucky mascot on Spirit Mountain. Then one day, he happened to hear the Buddha say, “That monkey's useless now. Get the next one.”
In that instant, all his memories came flooding back.
Then he died, not from being beaten to death, but from being crushed by the “truth” itself.
Then he was reborn, returning to the first year of his imprisonment beneath Five Elements Mountain.
During his five-hundred-year “vacation,” he relived every moment of his previous life over and over, worked through every detail, and calculated every turning point.
This time, he wouldn't become a Buddha. He would make sure everyone was free.