Edit: I am not trying to be snide, but you don’t actually have to talk to people to get an understanding of their viewpoint. Try reading some books from the far left and far right in the US and you will start to see how the other side thinks. Heck even tuning into Fox News, NPR, and the BBC in the same news cycle is useful.
The problem with using only books to try and understand what people who are disagree with you think is that they aren't interactive. While reading something you disagree with, you will probably find yourself thinking "Well, what about X", and if the book doesn't explicitly address that issue you will never know what they would respond. Even worse, people tend to assume that those who disagree with them don't have an answer to their objections, rather than that the book simply doesn't address them. If you are instead talking to a (reasonably knowledgeable) person, they will be able to at least give some sort of answer to your objections.
That's true. But it's more meaningful from the societal level than the personal. As an individual looking for interesting or useful things you don't already know it's usually far more efficient to read a few books than to spend the same amount of time getting to know people outside your circle.
Now if you want to learn something that a large number of people don't already know then goes treasure hunting. But, suggesting people need to talk with a wide range of people to grow as a person is simply untrue.
Edit: I am not trying to be snide, but you don’t actually have to talk to people to get an understanding of their viewpoint. Try reading some books from the far left and far right in the US and you will start to see how the other side thinks. Heck even tuning into Fox News, NPR, and the BBC in the same news cycle is useful.