Why do protestants believe in Sola Scriptura?

Why do Protestants believe the only source of truth is the Bible, given the clear contradiction to that idea you made? Do they not believe in the trinity either? (see How can the Church teach things not found in Scripture?)

When Luther seperated, one of his mottos was "Sola Scriptura". I don't think he forsaw the difficulties this would raise. Protestants read the bible, come to a conclusion, and when they find out that The Catholic Church has a different conclusion, they say 'well the Church must be worng'. So basically, they have to keep believing in just the Bible, or change too many other things they believe in!

Luther still believed in the true presence of Jesus in the Eucharist (though slightly different than Catholics)- but even in his day, Calvin and Zwingli came to different conclusions using the Bible alone- so they formed new denominations! Nowadays, there are thousands of protestant denominations all with their own teachings- all using 'just the Bible'!

So, most of them still believe in the Trinity, but not all. Jehovahs Witnesses (usually not considered a denomination, but a cult) think Jesus was St Michael the Archangel, and not God. The United Church officially stated that they don't know for sure.

The problem is they grow up proving everything they believe in scripture to each other, and learn to argue so intensely from the Bible that they never even ask the question if it can stand alone or if the Bible ever intended to teach on things like the trinity. Catholics do this too, so that when Protestants ask us to defend our faith, we show them scripture passages that support our teaching, even though at the end of the day some of the passages were not written to do that. We basically treat scripture like a countries constitution- a basis from which to debate. And we read it like we're a bunch of lawyers. This is not how Catholic have traditionally read scripture- it is not to argue about theology, but rather to come to know the person who is God. This is why we ordain preachers- so that we can say they officially represent what the Church has to say, and we know when we hear a preacher that they are not just spouting off their opinion!