When we seek evidence that only supports our opinions and ignore contradicting information.
Confirmation bias is when having formed an opinion, we both favor and seek out evidence that supports our opinion, and overlook or discount contradicting evidence. We all favor ideas that confirm our existing beliefs. Gerry is suffering from confirmation bias if he believes his snowmobile route is safe today, and uses other riders’ tracks on the route as evidence to support his decision while overlooking a fresh avalanche that crossed the road he was on. Gerry is looking to confirm his own belief so he puts more weight on the evidence that supports it.