For example we see a fire truck and say it is red. But is it? The brain does not actually see the colour red. What it accepts is the wave oscillation of light reflected off the fire truck and that light contains all colours except red. in other words it is the absence of red that makes the truck appear red. So as you look at reality what you are looking at is everything other than what is there. The point is that what you believe to be reality or truth is the absence of reality translated by your brain from a wavelength into what seems to be undeniable truth...the fire truck is red,I will stake my life on it...and then all the people seeing it say the same thing so you have confirmation of that reality. Reality is in fact subjective and truth is as numerous as there are people on earth...