Practicing critical thinking.

Many here have already recommended reading and, particularly, reading philosophy. That’s a great way to practice critical thinking and to practice thinking outside of our comfortable or familiar ways. I’d add not to skip reading about logical fallacies and cognitive biases.

Many good things come from being a little cautious with apparent knowledge. To keep a reasonable doubt is also to keep our curiosity going, to keep asking questions, to imagine different ways, to discover new things, to avoid stagnant beliefs, etc. Critical thinking makes us not only less gullible but also flexible. This is valuable to understand everything, including one another, and perhaps in doing so, giving us better relationships and better societies.