How about this: In order to observe, we need an observer (subject) and an observed (object). Therefore, objective observation is a contradiction in terms, because it would require an observation without an observer.
The/our brain is the observer prior to us being consciously aware of the observation.
Consciously, what we observe is not reality. It is a prediction of what reality is structured in a format that is easily understood by our conscious awareness so we can, usually, effectively interact with this reality.
Or how about this: Our sensory organs are only capable of receiving very specific types of data, and no others.
Therefore, all sensory data we receive is already filtered through the capabilities and ideosyncracies of our sensory organs.
objective here is the definition of objective I believe applies - b: involving or deriving from sense perception or experience with actual objects, conditions, or phenomena
Do you believe that our sense perception is not derived from actual physical objects?
Or how about this: The fact that we perceive reality in a structured, patterned way that makes intuitive sense to us suggests two possible states - either reality is already structured and patterned so that we can make sense of it, or our minds pre-structure and pre-pattern all our impressions of reality so as to make intuitive sense of it; in either case, our perceptions of reality are being structured in exactly such a way as to conform to our subjective understanding of it.
Yes, our brain uses a subconscious process to predict a reality and present it to our conscious awareness that has developed since we were first born. This does not mean our brain does not receive objective sensory in formation. Only that if it does, we are not directly aware of it. Because of this we have learn how to trick the brain into seeing reality as something it is not through optical illusion as was previously presented. This doesn't mean the non-conscious part of our brain was fooled by the objective sensory date we received.