Originally Posted by guiri
Read it somewhere, it has something to do about not being part of the background view.
All things moving at the same speed, in the same direction become part of the background visually. Part of the reason that people tend to say that they looked but didn't see the motorcycle, it just blended with the background and being smaller than the vehicles around it simply disappeared.
So ... if you are moving at a different angle, or rate of speed from ( I like 5-10k faster than the flow ) you have a better chance of being seen. Ever look at something in wide view and you only noticed the animal when it moved... kinda the same thing
Someone is going to have a more detailed / better explanation.. But that's my 2