Everything is interpreted by the mind and so I think that technically reality itself is subjective. For instance, someone might verify a tree exists by seeing the tree. Their eyes take that sensory information and project it to the brain. Their brain then interprets the information and as a result they see a tree. One can further enforce their conviction that there is a tree by touching it, smelling it, tasting it or hearing it. To finalize their conviction they can ask if anybody else sees the tree. Chances are highly likely that everyone will also see the tree. Therefore, there’s plenty of reason to believe that the tree exists and that the existence of the tree is a matter of knowledge rather than belief.
Pretty well anyone who doesn’t see the tree is either lying or mentally unstable and in either case I highly doubt that a person would be able to walk through a tree just because they didn’t believe it was there. However, the tree might not be there because the only way I can confirm whether or not someone can walk through a tree is through the use of my perceptions. Furthermore, I cannot confirm that the people who also see the tree aren’t figments of my imagination.
Without an objective basis for measuring reality, (a method that doesn’t rely on our senses), knowledge is really nothing more than a strong, seemingly undeniable conviction free from persuasive counter arguments. (Whether or not a counter argument is persuasive is a matter of personal judgement).
I do not regard myself to be a nihilist or existentialist, because I don’t necessarily support the idea that there is no objective basis for life. I support the idea that a person’s experience of reality is subjective, but I can’t come to the conclusion that reality itself is subjective. I cannot prove without the use of my possibly unreliable senses that sights, sounds, tastes, scents and touches exist outside my head, but I cannot deny the existence of myself so there must be some form of reality not neccessarily apart from myself, but apart from my perception of myself. I can’t dwell on the matter forever though, because I feel that I must base my perceptions on something. Yes, all fact is the result of belief and all belief is the consequence of perception formulating itself in the mind, but the mind has to believe something less its consciousness lose its significance.