What scientific concept would improve everybody's cognitive toolkit?
Jan. 19&24 update: built a cleaner user interface to the answers (on a new blog at worldquestionseriesplus.blogspot.com), and more (expanding the in-group (*), it does include Tobis's Coherence.)
I haven't read through all the answers yet; will likely add more highlights here once I've done so, or feel free to add your favorites in comments below.
Carlo Rovelli (Physicist) nominates The Uselessness of Certainty:
"There is a widely used notion that does plenty of damage: the notion of "scientifically proven". Nearly an oxymoron. The very foundation of science is to keep the door open to doubt. ... Failure to appreciate the value of the lack of certainty is at the origin of much silliness in our society. Are we sure that the Earth is going to keep heating up, if we do not do anything? ... Every knowledge, even the most solid, carries a margin of uncertainty. ... [If] from this lack of certainty we jump to the conviction that we better not care about global heating... well, we are simply stupid.
Better understanding of the meaning of probability, and especially realizing that we never have, nor need, 'scientifically proven' facts, but only a sufficiently high degree of probability, in order to take decisions and act, would improve everybody's conceptual toolkit."
Added 2011-01-24: Also see William Calvin's Find That Frame
Added 2011-01-17: Tobis adds the concept of Coherence:
... our ability to advance the truth is based fundamentally on our understanding the truth well enough to quickly discard most untruths. Constructing a realistic and productive perspective is a matter, like the sculptor removing all the marble that is not part of his subject, of getting good at throwing away the stuff that doesn't matter....[which is] is the stuff that is incoherent with what is already known.
Jan 19: & in comments there at Tobis's, I've added "Type I vs Type II errors" (link); though this answer may (still) already be among the ones provided.
Previous NCFocus posts on Edge's World Question Center, with favorite answers, in Jan 2004, Sept 2004, Jan 2005.