I'm aware of how unaware I am
The most profound lesson I've assimilated is that I'm aware of how unaware I am. Our beliefs, theories, truths, facts, reality, you name it - are fragile and depend on the transitory perception of an ephemeral creature drugged by its own chemistry; hallucinating this experience. It's all subject to change, and probably does alter as we change, which indicates whether there is anything other than what we perceive.
In thought of this, consider the simulation hypothesis, an idea that we're inside a computer-related construct. However, take it a step further. Computers and simulations are relative to the current technological period of our civilisation. The theory could not have existed without first the imagined idea and words of both computer and simulation. In my opinion, if you seek a more plausible simulation theory, this is it - we simulate this world from our imagination through art, language and expression. It's often forgotten that reality is a product of the imagination - that what we now define as real once existed solely in the unreal; they are opposite sides of the same coin.
Therefore, know the world you live in now will not be the world of tomorrow, and that's why it's crucial we do not cling to anything. Otherwise, we will be lost in time.