"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.

Here's a video explanation:

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. 

For example, someone who has become a Christian in a particular church will feel a strong attachment to that church and its particular beliefs, especially if the pastor keeps reinforcing those particular beliefs, week after week. In many churches, the Sunday service is specifically geared towards reinforcing the importance and validity of that church, and its particular beliefs.  How many times have you heard testimonials about how wonderful your church is? Add in some emotional background music to those tearful stories and it becomes almost impossible for anyone to objectively evaluate the things being taught. Is your pastor and/or church teaching sound doctrine that actually comes from the Bible? Most people want to believe that, yes, their church is really Biblical, and usually that's all that is necessary: if you really believe your church is Biblical, you'll never check your Bible to see what God's Word actually says. And if you're presented with Biblical evidence that threatens your beliefs, you'll ignore it and explain it away. To do otherwise would be very uncomfortable.

An unwavering belief in your church and your pastor is, all too often, a self-contained cluster of presuppositions based on years of personal experience. What does that personal experience entail? Much of it is listening to your pastor at your church tell you how to understand God, the church, the Bible... pretty much everything.

This kind of "thought loop" is very hard to escape from because it's a type of blindness that disguises itself as clarity and certainty.

Additionally, the emotional tug of nostalgia often prevents you from learning the truth. If you've formed your essential spiritual beliefs at a church where you have fond memories, you will probably ignore whatever false doctrine you might have learned there; in fact, you will defend that false doctrine regardless of what the Bible says. But please understand:

God's Word is high above the teachings of any man, and your emotional attachment to any pastor, teacher or church needs to STOP at the very point where the two collide.

Are you interested in finding out if what you believe is actually in the Bible (or not)? Here's an article where a bunch of commonly held "Christian" beliefs are compared with the Bible: 

"Bible-Believing" Christian??

On the subject of nostalgia, have you noticed how pastors will preach "sermons" with topics that will appeal to your feelings of nostalgia? "Gag Me With A Spoon: An 80's Approach to Knowing God's Will" is a fake sermon title I just made up, but it might as well be real. The exaggerated claim to "make Christianity relevant" is most often just an attempt to keep you: 

• showing up (for the entertainment/spectacle/novelty),

• signing up (you better get involved, because you've been sent on a guilt trip) and finally,

• shutting up (because you've been told to be an obedient part of the team).

Your function is to conform to the pastor/leader, and then he confirms his particular beliefs week after week (as he waves a Bible around like a prop). This is how the monster of your confirmation bias gets well fed. 

On top of this appeal to your nostalgia is the even more emotional appeal (and near-constant repetition) of the worship songs. Is it really necessary for the praise band to repeatedly play the Dsus, Em7, C2 chord progression quietly in the background while the pastor wraps up his sermon? Yes! How else can a non-Biblical point be reinforced? How else can you "feel" the Holy Spirit? This is Manipulation 101, and it's a form of hypnosis.

If you've read this far into this article and these ideas are new to you, you're possibly experiencing some "cognitive dissonance." This is what happens when we try and hold two different beliefs at the same time; it's like saying "I believe two plus two equals four, but I also believe it equals five." Our minds have a hard time doing that (which is a good thing!), but we tend to blame someone or something else instead of admitting that one of the thoughts has to be deleted. Here's an article that goes into more detail about this:

Cognitive Dissonance and the Silly Putty Jesus

Most Christians will proclaim that they believe the Bible, first and foremost; and they're certain that their pastor or favorite teacher is following the Bible, too. If that describes you, let me issue a challenge to you (see if this applies to you):

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.

• They are getting filthy rich, flying around the world and living like rock stars.

• They are accountable to no one, except a board full of yes men (often other mega-church pastors).

• They live luxuriously in gigantic mansions.

• They teach the false doctrine of "tithing as proven investment scheme" in order to get your money.

• They manipulate people by constantly claiming to "hear from God," while ignoring and/or twisting God's actual Word.

• They make millions on the conference/book-selling circuit because they are part of a "club" where they speak at each other's mega-churches and receive sacks full of tax-free cash they call "free will offerings." That's also why they never criticize each other ("you scratch my back, I'll scratch yours").

• They don't actually study the Bible very much, instead they focus on make convincing speeches that continue to suck people into the bondage of false teaching. Hyper-emotionalism, made-up stories, plagiarism, stand-up comedy ripoffs... whatever works.

• They are driving people away from true Christianity and setting them up for a life of deception, confusion, false promises and a false Gospel.

Maybe it's time for you to take a stand and agree with the "Manifesto of Christian Discernment"

Here's an amazing sermon/article written in the mid 1800s by C. F. W. Walther called, "The Sheep Judge Their Shepherds;" which is even more applicable for today's church.

Here's an article to help you see through all the deception in the church today: Defusing Demonic Dirty Bombs.