It is actually Satan who blinds unbelievers
2 Cor 4:1 Therefore seeing we have this ministry, as we have received mercy, we faint not;
2 But have renounced the hidden things of dishonesty, not walking in craftiness, nor handling the word of God deceitfully; but by manifestation of the truth commending ourselves to every man's conscience in the sight of God.
3 But if our gospel be hid, it is hid to them that are lost:
4 In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
The gospel, the truth of God is preached (manifestation of the truth) to every man. It is only hidden to those who are lost, who are blinded by the god of this world (Satan).
But the fault is their's.
2 Thess 2:8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
11 And for this cause God shall send them strong delusion, that they should believe a lie: 12 That they all might be damned who believed not the truth, but had pleasure in unrighteousness.
Because some people do not want to believe the truth, and because some people love sin, God allows them to believe a lie.
Rom 1:19 Because that which may be known of God is manifest in them; for God hath shewed it unto them.
20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:
21 Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
22 Professing themselves to be wise, they became fools,
23 And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things.
24 Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves: 25 Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen.
26 For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:
27 And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet.
28 And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient;
Have you ever heard someone say when disagreeing with someone "I give up! You are never going to listen!" I assure you parents say something like this to teenagers every day of the week.
And even here we often say, "Believe what you want", in fact, a poster here said that very thing to me the other night.
Well, that's how it is with God too. It is his will that all be saved. The gospel is preached to all, but some will not hear. So in effect God says, "I give up!, believe what you want."
And you can tell a teenager how important it is to study and make good grades. And they will act like they do not understand you. They will tell you how boring and useless school is. You see, a person can deceive their ownselves and often do.