What convinced you that sola scriptura is wrong?

When I was about 24, in college, I took a class on Eastern Orthodoxy and church history, and the process was deeply unsettling, because I realized what I believed was not in line with what the early church taught. One of the five core tenets of the Reformation is sola scriptura, the authority of scripture. But my professor, a Protestant, explained that the New Testament was not codified for about 300 years, people were illiterate, duplicating the apostles' writings was expensive, and whatever people had was read in church by those who were literate.

People weren't at home studying their Bibles. I realized in that moment there's no way sola scriptura is true, because for hundreds of years that practice didn't even exist. Then I encountered the Orthodox claim: the Bible is an authority, but not the ultimate authority, because every time you read the Bible it requires interpretation. Who provides the interpretation, and how do you know it's correct?

In my six years as a Protestant I had changed my theological views over time while reading the same Bible, and I thought other Protestants were wrong in their interpretations too. The Orthodox claim is that the authority is the church, which interprets the Holy Scripture under the guidance of the Holy Spirit, and that is what creates sound doctrine. In the past I would have said the Bible was my authority, but really it was my interpretation of the Bible. So in actuality, I was the authority, because I was the one interpreting it.