Following up the blog yesterday about the hate campaign against Comic Sans, I would add that instead of passing judgement about something based on our own conviction, it may be better to also take the context into consideration.
Take the following picture as an example (Picture credit: Beau Lotto at http://www.lottolab.org/index.asp).
Look at the two circled tiles. Even now, when I know the absolute truth that their colour is identical (I've confirmed this through the reading provided by my graphic design software), my brain keeps refusing to accept it. It is so "obvious" that the one in shadow is bright orange whereas the one under bright light is dark brown.
So in some cases our brains are so naturally attuned to situational factors when we judge what we perceive, such as colours, size, angles, light and shade, that we even subjectively reject what objective measures inform us. These are the situations where we are so easily fooled by illusions.
The message is very clear here. We make sense of the world and we function by considering, knowingly or unknowingly, the contextual information. That is how much of our judgement should be based.