The most formidable weapon against errors of every kind is reason.

Mistaken beliefs are rarely dislodged by force or by mockery, both of which harden them. What actually works is slower: laying out the reasoning, checking it against what can be observed, and being willing to follow it somewhere you did not intend to go. The method is unimpressive in any single argument, and it is the only thing that reliably accumulates.

Apply it inward first, since your own errors are the ones you have most access to. Take a factual belief you hold strongly, about a person, a plan or how something works, and ask what evidence would change your mind. If nothing would, it may be resting on something other than the evidence, and it is worth knowing what.