Summary: Is it possible for us to deceive ourselves into believing what is false? God says it is...
People can delude themselves into believing whatever they want.
For example, before I became a Christian (when I was 21), I was out driving my truck when I needed to turn around and go back to where I left. When I did so, I backed into a street sign and scraped up and dented my truck. Of course, I thought I would get in trouble for this, so I invented a story saying that someone hit my truck in the Wall-Mart parking lot. I had repeated this story that I knew was false so many times over the following months that it got to the point that I actually believed that it happened. Whenever I would talk about, it would become second nature, like this is really what happened. The cliche is right that says that if you repeat a lie enough times, you are going to believe it. You can deceive yourself into believing what is false.
Self-deception is a common thing that happens in some way to all of us, especially when it comes to trying to justify or rationalize something that we want to do that may be contrary to the will of God. This is even more true when it comes to those who claim that they do not believe in God. I have been spending a lot of time recently studying atheism along with ways of refuting atheists. As I have studied things that they believe, and as I have been learning things in school about what "science" teaches about the origins of the world and of life, I have seen one thing really clear: some people will put in a ton of effort to reject God, and when they do this, they are willing to believe almost anything so they can suppress the truth that God so clearly shows all of us about His existence in His creation and in His word.
God says that this will happen to those who don't want to submit to Him. This is so clearly seen in Romans 1:18-32:
"For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, 19 because that which is known about God is evident within them; for God made it evident to them. 20 For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. 21 For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. 22 Professing to be wise, they became fools, 23 and exchanged the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures. 24 Therefore God gave them over in the lusts of their hearts to impurity, so that their bodies would be dishonored among them. 25 For they exchanged the truth of God for a lie, and worshiped and served the creature rather than the Creator, who is blessed forever … 32 and although they know the ordinance of God, that those who practice such things are worthy of death, they not only do the same, but also give hearty approval to those who practice them" (Romans 1:18-25, 32).
God says in this text through the Apostle Paul that sin is very deceptive. Those who love it and do not want to give it up will do all that they can do continue it. They learn to worship and serve themselves. They suppress the truth in their unrighteousness (21, 32) and reject the God that they know exists (21). The end of such a path is vanity. When people reject God, they walk in darkness and in the futility of their foolish minds (21). When people profess to not believe in God, what I have seen when you press the issue a little bit is that their rejection of God is not an intellectual one, but a moral one.
Why does Psalm 14:1 call the one who says that there is no God a fool? The reason seems clear to me. It is because they are suppressing what God has made so clear. They are suppressing all of the treasures of wisdom and truth that are found in Christ to live in futility. But Paul makes it clear, they are without excuse for denying our God who has made Himself and His power so clear.
This is what our sin will lead to if we don't take care of it. Sin can have a hardening effect on our lives.
WE ARE NOT EXEMPT!!!
We ourselves do not realize at times just how terrible sin is and what it can do to our hearts. Just little by little, sin can drift us away from God. It will harden our hearts. it can be like yeast that leavens the whole lump of dough.