What is the belief bias?

We judge whether an argument is sound by whether we agree with its conclusion, rather than by whether the reasoning actually holds.

The mechanism is that evaluating logic is effortful, so the brain takes a shortcut: if the conclusion feels true, the argument seems valid; if the conclusion feels false, the argument seems flawed — regardless of the real logical structure. Believability gets substituted for validity.

Example: "All living things need water; roses need water; therefore roses are living things." The conclusion is true, so it feels like a valid argument — but the logic is actually broken (it's the same form as "all cats have legs; dogs have legs; therefore dogs are cats"). We wave it through because we like where it lands.

Tip: To test an argument, temporarily ignore whether you agree with the conclusion and check only whether the conclusion must follow from the premises.