As riders, we hear it all the time that bikes are hard to see. We hear that we should be wearing bright clothing and hi viz to make ourselves more visible.
There's a growing body of evidence that says that the issue is not with riders, but with the human brain, particularly those of drivers engaged in the act of driving and prone to something called "Inattentional blindness" and "Change blindness".
What that means is that when a bike enters a driver's field of view, the change is small enough that the brain registers it as irrelevant and not worthy of note so it filters it out. It's not until the bike takes up an unavoidable amount of the field of view that it is finally cognitively recognised and the bike is said to have "Come from out of nowhere!".
Humans "see" an image pieced together by the brain from the signals that come down the optic nerve. The brain does a masterful job of filtering out "noise" and creating a small zone of great detail where a predator needs it the most, front and centre. It guesses/"makes up" the rest of the vision field with approximations and expectations.
All the above, plus a number of other physiological and cognitive "features" of the brain mean that a small foot print vehicle like a motorcycle can be for all intents and purposes INVISIBLE on the road.
One countermeasure to this is awareness - drivers see what they expect to see and/or are aware of. There are demonstrations of this everyday where family and friends report suddenly seeing bikes everywhere when a loved one takes up riding. Those bikes didn't suddenly appear, they've always been there. This is the awareness in action.
Check out this video to start getting an insight into just how fallible vision is. Never assume you have been seen. Never rely on being seen. Ride like you are invisible.