That is subjective opinion based on the idea that the Catholic Church cannot be right where it is different from the accepted "less fallible" opinion of the Protestant. The theory still stands. You are "more right" than the Church, a claim that has very little supporting evidence. Yet, it is held as an infallible doctrine - the mere fact that you are "more right" than the believing Church of 2000 years. Unfortunately for this idea, there is no supporting evidence, just hearsay and opinion.
It comes down to proper interpretation. Who holds it? That is a question that was pondered from the beginning. Even in the Sacred Scriptures, we find this question coming to the fro. Clearly, the Bible and extra-biblical writings of the first few centuries express that the CHURCH has the "right reading" of the Bible. Thus, the Church is infallible. The evidence is the bible and the men who wrote it.
The early horrid fallacy
that the 1600 year old RC edifice = THE CHURCH UNIVERSAL
is the source of all kinds of error.