Driving my kid into Toronto from Mississauga, I turned southwards at a major intersection. I saw three or four pedestrians at the corner to the right of me, checked the cross walk and the traffic, and turned. As I headed south, I looked in the mirror and saw three bicycles in the cross walk. It brought home to me how quickly a bicycle can travel from outside the range of a driver's scan, and how cyclists make it difficult for drivers to see us when we act as pedestrians do.
It put me in mind of another time, driving through a wall of rain in the late evening, straining to see, a shadow passed in front of me. I braked. Of course, I had come close to a cyclist riding at night and in filthy weather without a light or much of a reflector. Once again, when cyclists do that, we make it very difficult for drivers to see us.
Of course, cyclists have to worry that even when we do everything right (lights on, signalling) drivers will either not see us, or else act as though they do not. This affects me as a cyclist most when I go to change lanes; when I signal for a lane change, I always have to wonder if the cars behind me in the lane I want to change to will slow down for me. I have certainly had cars speed past me while I signalled and tried (in vain) to shift lanes.
As cyclists, we need to make ourselves visible in traffic. As drivers, we need to make an effort to see all road users.