The passenger reading directions is carrying a responsibility the driver cannot safely absorb alone.

Two people in a car are running one task between them. The driver is holding speed, traffic, and the road surface, which leaves very little spare attention for the next turning, so the passenger is not helping with a job but doing part of it. Treating that as a minor courtesy is how it ends up done badly and blamed loudly. Shared work goes wrong when only one half of it gets named.

On the next drive, agree who is watching the route before you set off. Say the turn early enough to be useful, and let being occasionally wrong be part of the arrangement.