What scientific concept would improve everybody's cognitive toolkit?

The question "What scientific concept would improve everybody's cognitive toolkit?" is Brockman's edge.org annual question. See http://www.edge.org/annual-question/ where it is addressed by many different authors. See:

http://news.ycombinator.com/item?id=2135504 http://news.ycombinator.com/item?id=2106857 http://apps.ycombinator.com/item?id=2540390 http://apps.ycombinator.com/item?id=2107720

and so forth.

That nothing in Science is 100% certain and it's a good idea to not get religious about it.

Definitely falsifiability. http://en.wikipedia.org/wiki/Falsifiability

Falsifiability is essentially irrelevant to 90% of people.