Context is crucial ! 
The "real" World
So far, we have seen that, for something which we consider in isolation (i.e., out of context) we can attribute an absolute value, or measure, etc.
But consider something in context, whatever the thing or the context, and the thing is likely to vary relatively to the context it is immersed in.
So has been the situation regarding the two lines, which we experience as different, or the water in that central bucket, which each hand experiences as different, or the teal color, we've just discussed. The water is the same, the lines are identical, and so is the teal color – at least so they all are if appraised in isolation (i.e., out of context).
What is the correct solution to this dilemma? What is the correct way of putting it?
Shall we say that the teal color is a single color, or that it varies? That the lines in the earlier example are identical, or that they vary? That the temperature of the water, in the other previous example, is constant throughout the bucket, or that it varies?...
In other words, is the value of this teal color, the length of the lines at stake, the temperature of the water, absolute or relative?
Both answers are correct, depending on whether you are going to deal with the teal/line/water all by itself or in context!
In the real world which we experience, the truth is that we hardly ever (if at all) face anything in isolation. Absolute concepts or definitions, however logically sound they may be, are not exactly akin to the World of Human experience.
Relativity thus goes a lot beyond the equations of physics, as we can see: it pervades the entirety of our lives, for we live immersed in contexts, which are, in turn, immersed in larger and larger contexts!
So, just about all we experience, the "I" in each one of us experiences it from within a context – starting with our own psychological context, and the cultural luggage we carry along with us! On the other extreme, the Universe is the largest context we know of.
A special note is in order: 'Real' is used above, because the only real thing we, Human Beings, can rely on is our experience – i.e., what we experience is what appears real to each of us, as we have already seen!
Whether or not the "eye" is directly involved,
to the "I" within,
it is what we experience that we feel as "real."
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