On this plate sent by NASA on a Pioneer mission to civilizations whom it may concern, the receiver, can see (if it is endowed with optic recognition) the proportion of two beings.
For our human eyes those shapes are two white people, man and woman, naked (probably because they are inspired by Leonardo da Vinci's Vitruvian man), but decent.
One, rises a quinary limb in what looks to me, here on Earth, as a Red Indian salute of peace, a “Stop here!” warning, or a traditional moutza Greek insult. The human shape is proportioned to all the rest; or is all the rest, atom to Universe related to it?
This makes me reflect to the maxim by Protagoras of Abdera, the disparaged philosopher:
"Man is the measure of all things: of things which are, how they are, and of things which are not, how they are not" 
This is what he said, which piqued Plato to ridicule him because Plato believed that eternal ideas, not Man, are the reliable reference .
This saying is for me a metaphor of us being the unavoidable means of knowing; for knowing is done by knowers and nothing else. We understand the World in the manner we interact with it, by our own proportion, from our point of view, inevitably in our human terms.
Why be so defensive against this maxim? You do not want people to believe a metaphor, it is meant to be understood not believed. It is the spoon, not the soup. It is the finger that points, not the moon. Metaphors do not explain, they help. They offer a vivid representation for common sense to move, to give shape and familiar concreteness, to let imagination compare. In this case, we are the spoon, we are the finger, while the Universe is still as it is. Philosophers pleased however to see the "man-measure statement" as the universal root of moral relativism; I believe that it simply refers to a legitimate point of view, which does not deny universal reality but cares for what it means to us...
“Man is the measure of all things...” indicates that, for us, in our life-space, things count to us as much as they relate to us; they represent to us, compellingly, what they are mind-size for us and what they make to us, not in general, nor in themselves but in interaction with us.
The thing in itself is indifferent to the person as infinity is not our house. If the human looks at infinity from his own point of view he sees immensity, something inconceivable; infinity does not see anything looking at the human, because it does not look - man is a speck of dust in the blind eye of the Universe; if human looks at himself from the eyeless point of view of infinity he sees nothing of human interest.
Most advanced knowledge and technology, giant discovery for Humanity, is still a small step for each single Man; the individual’s legitimate question is what use, what meaning it gives to our life. I compare this with immensity that disenchants us humans and leaves our life meaningless. Our question is what wisdom we gain to live happier.
For wisdom is a humble choice; of looking at us and the world and interpreting the encounter steadily from the point of view of what it is to us as persons, of what makes sense to us, of what value it has for our life: How does it concern people? Is it good for me or bad for me? Do I like it? What can I do about it? What is best for us to decide, to do, to beware? From where do we come, who are we, where do we go?...
Such purposeful “anthropocentric bias” makes knowledge human, ours, understood beyond parroted grand explanations. The rest, so necessary, so undeniably true, so powerful - facts, data, experiments, objective explanation of things “in themselves” - is ascetic science and disinterested reason trying not to be human, craving to free itself from being human; that is, truth for a world without us. That knowledge, independent of us, its capital discoveries and its planet-changing technological conquests, require constant vigilance and harnessing to join back our best interest.
Let us be clear, humane wisdom is not opposed to science; it is its necessary complement (even as science does not know yet how to define it and serve it in its conclusions). It would be of course absurd to say that wisdom is better than science. The vocation of wisdom is not to diminish our trustful respect for science; it is rather to grant that science still serves us, instead of us worshipping science.
Wherever science prevailed, wisdom is science translated in human terms, science plus an interpretation centred on the conscious human person, the one who feels, thinks, and says “I” knowingly.
We humans want to know things as they are and also to judge what they mean to us, not to the infinite Universe, nor for the sake of Ultimate Truth. This entails understanding the humble but ultimate human interest of living a good life: grasping what the known means for us, how it links to our needs and values and action.
The wise examine consequences of what we meet and do, for the earthly life of persons. They seek the ways to navigate the maze of the given, to chose, steer course and improve our earthly reality instead of just bearing it.
Where science fears to rush in, repelled by imprecision, flow, subjectivity and lack of "proper logic" (which describes fairly the human world), wise judgement navigates alone, subtle, intuitive, risky but life-saving.
A wise one works to turn the world mind size for us; fools make it too complicated to cope with; or too abstract, metallic and alien to us to live.
Be on your guard though to the power and dangers of making things simple. “Science without conscience" is a cold beast; but let us add with prudence: wisdom unverified is of a blind seer.
© Ioan Tenner & Daniel Tenner 2011-2017
 in Sextus Empiricus (Adversus Mathematicos, 7.60) (Diels Kranz 80 b1):
“Of all things the measure is man, of the things that are, that [or "how"] they are, and of things that are not, that [or "how"] they are not.”
Sextus Empiricus, Outlines of Pyrrhonism, 1.216; Diogenes Laertius 9.51.
About what the mysterious phrase may initially mean, it is useful to read Ugo Zilioli, Protagoras and the Challenge of Relativism: Plato’s Subtlest Enemy, Ashgate, Burlington, 2007
Hannah Arendt goes even deeper in restoring what Protagoras actually said:
""man is the measure of all use things (chremata) [my underlining], of the existence of those that are, and of the non-existence of those that are not." in:
Arendt, Hannah, The Human Condition, 2nd ed The Univ. of Chicago Press, 1998, p 157
Reading her interpretation I realise that the "being the measure" of Protagoras was about all things made (and maybe looked at) for the use of Homo Faber, in the life-space created by humans.
 Plato turned Protagoras into a straw-man for his equally extravagant contrary belief that absolute and eternal ideas (finally, God) are the measure (the norm) of all things; later philosophers thought that nay, Reason, not God is the measure and judge; nowadays, triumphant Science knows for certain that Matter, the Universe – in which we are nothing but dust of stars – is the real measure we must use.
 Rabelais: "..,.science sans conscience n'est que ruine de l'ame... Œuvres de François Rabelais, Tome troisième, Pantagruel, Librairie Ancienne Edouard Champion, Paris, 1922, ch III, p.109
PS: This outline was reviewed in 2012 and 2013, based on my discussions with Daniel Tenner.