You need to regularly hang out with people who disagree with you. They can have beliefs or views that are opposed to yours, or they can simply have more moderate versions of your beliefs, but ideally a mix is best. It’s really, really important.
One of the reasons it’s so important is that people who agree with you in a given area will generally not tell you when you’re being absolutely batshit insane in that area.
Partially it’s because tribalism makes us support people of our own tribe regardless of what they actually say. As long as the person is from your ingroup, you’re predisposed to view them sympathetically and, even if you disagree with them, keep quiet about any dissent.
But equally it’s because in-groups tend toward ever more extreme versions of their core views over time. Know your Maslow – once you’re in a group, you want status. And if the group’s “thing” is Belief X, then you gain status by claiming the most extreme version of X that you can stomach. The most extreme are thus the highest status and the Overton window moves over time.
But as your in-group’s views become more extreme, they deviate from society’s norms further and further. If you’re isolated in that echo chamber, eventually you’re saying or even believing things that are absolutely bonkers but gain you a lot of status with a hyper-narrow group. But your life will collide into “normal society” frequently, and if your most extreme bonkers views leak out – especially if you don’t realize that they’re looney tunes – you can have a real problem.
The solution is cosmopolitanism. You don’t have to dilute your deeply-held beliefs, but you should know where they fit. You should know which things are considered the absolute craziest, even if only out of self-preservation. You should challenge your wildest ideas and be able to defend them against the challenges from the middle of the Bell curve, or you shouldn’t have them.
Talk with many people. Sharpen your wits, stabilize your emotions, and control your beliefs (rather than the reverse). Otherwise, you won’t even know what your problem is.
The Opportunity Machine 