The Oracle of Delphi famously pronounced Socrates to be "the most intelligent man in the world because he knew that he knew nothing". Over 2000 years later the physicist-turned-historian Jacob Bronowski would emphasize — in the last episode of his landmark 1970s television series the "Ascent of Man" — the danger of our all-too-human conceit of thinking we know something. What Socrates knew and what Bronowski had come to appreciate is that knowledge — true knowledge — is difficult, maybe even impossible, to come buy, it is prone to misunderstanding and counterfactuals, and most importantly it can never be acquired with exact precision, there will always be some element of doubt about anything we come to "know"' from our observations of the world.
What is it that adds doubt to our knowledge? It is not just the complexity of life: uncertainty is built in to anything we measure. No matter how well you can measure something, you might be wrong by up to ½ of the smallest unit you can discern.
If you tell me I am 6 feet tall, and you can measure to the nearest inch, I might actually be 5' 11 and ½" or 6' and ½" and you (and I) won't know the difference. If something is really small you won't even be able to measure it, and if it is really really small a light microscope (and thus your eye, both of which can only see objects larger than the shortest wavelength of visible light) won't even know it is there. What if you measure something repeatedly?
This helps, but consider the plight of those charged with international standards of weights and measures. There is a lump of metal stored under a glass case in Sèvres, France. It is, by the decree of Le Système International d'Unités, the definition a kilogram. How much does it weigh? Well, by definition whatever it weighs is a kilogram. But the fascinating thing is that it has never weighed exactly the same twice. On those days it weighs less than a kilogram you are not getting such a good deal at the grocery store. On other days you are.
The often blithe way in which scientific "findings" are reported by the popular press can mask just how difficult it is to acquire reliable knowledge. Height and weight are — as far as we know — single dimensions. Consider then how much more difficult it is to measure something like intelligence, the risk of getting cancer from eating too much meat, whether cannibas should be legalized, whether the climate is warming and why, what a "shorthand abstraction" or even "science" is, the risk of developing psychosis from drug abuse, the best way to lose weight, whether it is better to force people receiving state benefits to work, whether prisons work, how to quit smoking, whether a glass of wine every day is good for you, whether it will hurt your children's eyes to use 3D glasses, or even just the best way to brush your teeth. In each case, what was actually measured, or who was measured, who were they compared to, for how long, are they like you and me, were there other factors that could explain the outcome?
The elusive nature of knowledge should remind us to be humble when interpreting it and acting on it, and this should grant us both a tolerance and skepticism towards others and their interpretations:knowledge should always be treated as a hypothesis.
It has only just recently emerged that Bronowski himself was involved in the Second World War project to design nuclear weapons — vicious projectiles of death that don't discriminate between good guys and bad guys. Maybe Bronowski's later humility was borne of this realization — that our views can be wrong and they can have consequences for others' lives.
Eager detractors of science as a way of understanding the world will jump on these ideas with glee, waving them about as proof that "nothing is real" and that science and its outputs are as much a human construct as art or religion. This is facile, ignorant and naïve.
Measurement and the "science" or theories it spawns must be treated with humility precisely because they are powerful ways of understanding and manipulating the world. Their observations can be replicated — even if imperfectly — and others can agree on how to make the measurements on which they depend, be they of intelligence, the mass of the Higgs boson, poverty, the speed at which proteins can fold into their three dimensional structures, or how big gorillas are.
No other system for acquiring knowledge even comes close to science, but this is precisely why we must treat its conclusions with humility. Einstein knew this when he said "all our science measured against reality is primitive and childlike" and yet he added "it is the most precious thing we have".