Why not? Do you think any sensible driver would overshoot/undershoot their speed by any meaningful amount without noticing? Like without a speedometer everyone would just accidentally go 100mph everywhere or something?

> of course. Any sensible driver will not drive the car without a speedometer.

I think you missed the point of my comment entirely.

Knowing your speed is not required to be safe while driving - being observant, correctly signaling, and driving at a speed appropriate for the conditions are.