Why don't people believe wet paint signs?

Answer 1

The problem with signs such as "Wet Paint" is that they eventually stop being true.

The road sign "Slow - Dangerous Bends' is permanently true,

and the Red traffic-light stops being true when it turns off

... but a "Wet Paint" sign stops being true after the paint dries, but the sign is still on display.

So, unless there is a smell of paint, or we have seen the painter at work, we have no real reason to believe the sign.