Do you only read books, online web pages, or newspaper articles that only reinforce your own opinions? Do you only talk with people who share your opinions and avoid those that challenge your ideas?
A political party is a good example. If you read an article on a political party that you support, will you stop reading it if the article is negative to your opinion? If the article is positive to your opinion, will you continue to read it? On the flip side, if you read about a political party that you don't support and it is negative to that political party, will you continue to read it? If the article is positive, will you stop reading it?
We live in a world where websites like to show us things based on our past search history, which often reinforce our own opinions.
If you have a problem, and you can't decide what to do, (but you kinda know what you want to do), do you keep asking for advice until you hear what you want to hear? This happens at work all the time where someone will go office to office until the advice they get is what they want to hear. Eventually they find someone who shares their opinion.
A true story. An elderly man with a bad knee wanted to have an operation to fix his knee. His doctor told him that he was too old for the surgery and would most likely die during the surgery. He went to another doctor who told him the same thing. Eventually he found a doctor would said he would do the surgery. As you can guess, he died during the surgery.
We can never grow as individuals if we close our minds to other opinions. Some people are so proud, their opinion can never change, even if what they believe in lets them down. (For example sport stars caught using steroids, celebrities having affairs, or politicians who get caught lying). We tend to approach discussions with the attitude that we are 100% right and as a result we don't listen to the other point of view. As we go down our path of opinion, we get to a point where we feel there is no point of return. Don't let your stubbornness blind you.
Everything (like this post) is an opinion. Nothing is exactly right (except math).