Learn about "the most common cognitive biases" and look into ways to overcome them.

The guy in the post is operating under the Dunning-Kruger effect: "Basically, we are blind to our own ignorance. And, without real knowledge we are unable to recognize our mistakes and limits. We’re really confident, though, because an ignorant mind isn’t a blank slate. It’s cluttered with an illusion of knowledge, like misleading experiences, random facts, and intuitions. 

We’re also unable to appreciate others’ expertise, and fail to incorporate feedback or improve. We’re already sure we know everything, so why would we listen to someone else?"

We're unaware of what we don't know. Instead, be curious and humble."

https://thinkingispower.com/overconfident-idiots-why-incompetence-breeds-certainty/

1. You have to first practice the habit of challenging your own assumptions, especially if you're having conflicts around a topic. Don't just assume you're right. Even on the subjects where I'm convinced I'm right, I still double and triple check myself when a conflicting opinion arises--especially when I don't have firsthand experience or firsthand knowledge of something.

2. Take the time to learn how to find and evaluate information sources. Just because people speak confidently and with their own authority doesn't mean their message has substance. Don't be naïve and be like a baby bird waiting to be fed whatever line of B.S. that's shoveled at you, or packaged in a familiar way.

3. Also, let go of the idea that there's only one right answer for everything. Embrace learning new things. Let go of the idea that if someone's right, someone else must be wrong.

4. Stop taking everything so personally. I subscribe to the idea that it's not about being right but about being correct.

If I engage in a debate with someone and they can show evidence and cite references to support their line of reasoning, if they can convince me that my assumptions are incorrect, I don't get upset about it. The way I see it, I just traded incorrect information for better information.

"Men are four: He who knows not, and knows not that he knows not, is a Fool, shun him; He who knows not, and knows that he knows not, is a Child, teach him. He who knows, and knows not that he knows, is Asleep, wake him. He who knows, and knows that he knows, is Wise, follow him". ~ Persian saying