It depends. Sometimes people have to witness or experience a revelation that emotionally moves them to change their beliefs.
Here’s an example of something like that that dramatically changed my best friend’s boyfriend’s ideas about being a vegetarian. Me and my best friend had been vegetarians long before she met him and started dating. He knew what it meant, and what it entailed. One day (this is now about 15 years ago) they were driving on a freeway in Los Angeles and witnessed a terrible traffic accident in which a truck full of live ducks was being transported to a slaughter house. A lot of the cages got hit by cars, and many of the animals were killed in the road, right in front of him. He became a vegetarian that day, and has been ever since. It was the emotional tragedy of the experience, that made him put his factual ideas about how animals are treated, with his visceral emotional response.
In other situations, people can change their own thinking by be willing to engage in the old adage “fake it till you make it.”
Imagine someone who goes to the doctor, and finds out that they have high cholesterol, they know they are overweight, but the doctor tells them that they are borderline obese, and because of that they are also pre-diabetic. The doctor suggests cutting out meat, and cheese, and highly processed foods, and refined sugar. So the patient starts a vegetarian or vegan diet, and ends up losing some weight, and feeling better. When the patient goes to the doctor again, the test numbers look much improved. The patient decides he wants to continue being a vegetarian.
These two situations are different, although the result (in this case, becoming a vegetarian) are different, but the motivation came from very different places, and because of very different experiences.