The way we gain physical strength is through resistance.
You need to regularly lift weights that are at the edge of your ability – and then, once those weights become easy, increase the weight. If you only lift weights you already can lift, you won’t get stronger. And if you don’t lift any weights at all, you’ll grow weaker.
I think the same holds true for mental strength.
You need to regularly interact with ideas and opinions you don’t agree with – and then, once you understand those ideas completely, try to understand ideas that are even more different. If you only consider ideas and opinions similar to your own, you won’t get smarter. And if you only ever consider ideas exactly like your own, you’ll get dumber.
The great thing about freedom of speech is that people you disagree with can speak their mind. Most people don’t realize this, but having people you disagree with speak openly ends up making you stronger – you have the option of listening to them, considering their idea, and then reacting to it. If you disagree with their opinion, your mind has become better trained, more capable of thinking about ideas in the future, and perhaps coming up with better reasons for why you believe what you currently believe.
If you accept their idea (which you’ll hopefully do sometimes), your beliefs will be better than they were before.
Be open-minded – just don’t be so open-minded that your brains fall out. There are plenty of ideas and opinions out there that are crazy, outdated, incoherent, or offensive. When you listen to ideas you disagree with, you have no obligation to agree, or respect the idea. But you should absolutely do your best to respect the person, their humanity, and respect their right to their own opinion – as they should respect you, your humanity, and your right to your opinions.
Talk to people you disagree with. Listen to people with different opinions than you. Consider ideas that are the opposite of your own. It is by listening to people with ideas different than ours, and seriously considering those ideas, that we become mentally strong.
And I want you to become strong.