We are not objective
I have been pretty much surprised when I see the flat LCD screen after watching a CRT tube, I find the LCD seemingly inwardly curved, but it is flat physically. which means I have a wrong perception of the reality. So it occurs to me that human's perception is not objective. Even though they saw with their very eyes but it may not be true in some aspect.
This observation tells that our perception is influenced by our experience and it is done automatically by our brains without notice. When we observe we are not just observing, our perception organ system has been making adjustment to the signals it receives based on previous experience and often present us a distorted picture, a wrong perception.
It means that we have perception inertia, we tend to form a picture with the signals we are familiar with, not as it is. We do put a meaning on what we see, not just re-representing it. That may create problems for us because different previous experiences may put different meanings on the same subject.
Are young children more objective than the middle-aged because they have less previous experience to lead them? When the situations have some major changes, don't let our past deceive us.
It is possible to be objective after a conscious effort to check perceptions. But this process is often omitted. That is why an open society is necessary when objectiveness is concerned. Because an open society provides more alternatives in experience, therefore more reference posibilities for perception.
No mater from what angle, we will not dispute the objective fact that human has two legs if we observe long enough, even though we may augue if human have pimples. So we can be objective on relatively large enough scale, but we can not be completely objective on any detail.