Put a compass next to a magnet and it’ll point the wrong way with total confidence. Watch what you stand next to.

Confidence is no guarantee of accuracy. A compass sitting next to a magnet points firmly and completely wrongly, and nothing in its behavior reveals the problem, which is exactly how bad influence works on a person. You do not feel misled. You feel sure, and the certainty arrived from whatever you happened to be standing beside.

Look at who you have been near when your opinions hardened lately. If a view of yours only feels obvious in one particular group, test it somewhere else this week and see whether it survives a change of room.