This question appeared on Quora once. I answered it like so:
Imagine my scenario:
You’re born into a family of a Jehovah’s Witness mum and dad.
Before you can even talk you’re trained to point at the sky when they playfully ask “who made the trees?”, “who made the grass?” etc and everyone goes “awwweeee!! That’s right!”
When you’re old enough to talk you’re encouraged to use the name Jehovah when talking about a magic man in the sky that watches us all and loves all of us Jehovah’s Witnesses.
At the age where you’re told that stealing is wrong, fire is hot, strange dogs are dangerous - you’re also told that there is a god called Jehovah and he has a son called Jesus. And that one day Jesus will kill everybody who isn't a Jehovah’s Witness and bring about a paradise on earth. You’re shown pictures in Watchtower literature of non Jehovah’s Witnesses. They’re evil. They all take drugs, sleep around, catch diseases. They gamble, smoke, drink to excess, get involved in politics, are corrupt, they live for pleasure and cannot be trusted. You’re also shown pictures of the world, the world is bad, evil, dangerous and is made to look enticing because Satan wants you to leave Jehovah. Then you’re shown more pictures (many pictures) of Jesus killing all of these people in a thing called Armageddon. But you’ll survive it if you become a Jehovah’s Witness. Again, you’re told this when you’re a little child. Before your critical thinking even has had a chance to develop.
From the age of about 3 years old you’re encouraged to put your hand up in the Kingdom Hall and give a one word answer in the book study or Watchtower study. Everybody goes “awwweeee!!” and you feel validated.
You, your friends and your family all refer to your religion as “the truth”. Cult experts recognize this as loaded language. It’s a well documented fact that if you repeat something to yourself enough you eventually believe it. So the idea that the religion you’re involved in ever being wrong simply does not compute.
You’re not allowed non JW friends. No birthday, no Christmas, no Easter, no learning about other religions in schools, you never learned the national anthem and you’re not allowed to study any other religious book unless it’s published by the Watchtower Society.
By the time you’re 12 you’ve already given many bible readings on the platform in front of an audience of about 70 people. More than likely you’re giving 5 min talks on various bible topics too. You’re given validation and praise. All this time you’ve also been out every Saturday morning and - if your family were very good Jehovah’s Witnesses, every Sunday afternoon too - knocking on peoples doors trying to talk to them about Jehovah and place magazines with them. This reinforces in your mind that you have the truth because why would 8 million people do this if it wasn't true?
By age 19 if you’re not baptized people will be wondering why, because surely you should know this is the truth by now? If you’re not baptized no girl will want to date you, you cant get married, your family will keep asking you why you’re not baptized.
So you believe it. And you believe it because you know of no other life, everyone around you believes it too so it must be right. And all the negatives about the world and people in it are blown out of proportion and their positives diminished. So you see the world as bad and cant wait for Jesus to destroy it and slaughter all those evil non JWs. When somebody online or on TV criticizes or poses questions you cant answer with Watchtower literature, or when the flaws in the religion are exposed you become very angry and defensive. You can feel the anger inside you like a burning blaze. This is cognitive dissonance at work.
So simply put, in my case is was slow, gradual, consistent indoctrination and effective mind control from a publishing cult in New York posing as a religion.
