First Rule of Italian Racing...

Starting at the one minute mark here.

I do not use mirrors on my bicycle for the same reason.

What's behind me doesn't matter. What is before me does.

The traffic conflicts for cyclists are from the same direction as for all other vehicles on the road. Primarily at intersections and junctions.*

Mirrors are not generally needed in automobiles unless one is preparing to change lanes or turn off the roadway. When traveling in a lane, they are not needed.

I have heard many folks advise cyclists to use a mirror to monitor overtaking traffic. Please! What an unnecessary distraction! The chances of a motorist running you down from behind if you are in the lane in front of them is vanishingly small. And by the time you perceived that you are in danger, it likely would be too late to escape. A whole lot of anxiety over an event that in practice will never happen. **

A mirror is no doubt helpful in preparing to merge left or keep track of riding companions, and for those who have difficulty turning their heads, so I am not saying that they don't have their uses. But to monitor overtaking traffic?

In front of me, I have road surface hazards, loose dogs, debris, junctions and intersections with cross traffic. Those are real and present dangers. What is behind me does not matter.

Once I have turned my attention away from the rear, I have less anxiety and enjoy my travels all the more. Perhaps Italian race car drivers have it right!

*I have adopted the practice of calling private and commercial driveways "junctions" and the where streets come together "intersections".

**Cyclists do get struck from behind while taking the lane. (I have just deleted four paragraphs of explanation. Obviously a rant for another day!)