The people of Israel forgot the Torah.

Hello, in the Book of Judges, chapter 2, verse 10, it is written that the people of Israel forgot the Torah, forgot the exodus from Egypt, forgot the presence at Mount Sinai.
After that, God sends a judge to lead the people and remind them of the covenant and their faith in God.
In other words, the Bible proves to us that one person can reach the people and make an entire nation believe in something.
So, how can we know that someone didn't come 2000 years ago and make the entire nation believe in his personal doctrine?
I am asking specifically about Rabbi Yehuda the President who signed the Mishnah. My claim is that he signed the Mishnah according to his personal perception and view, in accordance with his own interpretation only.
thanks.