“Confirmation bias” is the name for a very common trait that all human beings share. When we favor information that validates our pre-existing beliefs but refuse to consider information that threatens our pre-existing beliefs, we are demonstrating confirmation bias; other names are confirmatory bias, myside bias or subjective validation.
It is very difficult for people to change their mind; this is part of our fallen condition as sinners. There isn’t much difference between Christians and non-Christians in this regard; we all tend to stick with our pre-existing ideas (also called our presuppositions, the things we “pre-suppose”). On top of this common human trait is the way we stick to whatever “our group” says; especially when “our group” is closely connected to our essential spiritual development.
When you are confronted with undeniable proof that your favorite pastor/teacher is actually saying stuff that isn’t in the Bible at all, and when you discover that they’re actually contradicting the Bible, you will say something like, “Well… I know pastor so-and-so, and he knows what he’s doing; he’s a good man and I trust him!” When you are doing this, you are putting the teachings of a man above the Word of God. You are just exhibiting a spiritualized version of confirmation bias. Many of the most popular and famous pastors/teachers in the world of pop evangelicalism are “teaching for shameful gain the things they ought not” and they are getting away with it, all the way to the bank.