Popper concluded that the mark of true science was falsifiability: a theory is genuinely scientific only if it's possible in principle to refute it. This may sound paradoxical, since science is about seeking truth, not falsehood. But Popper showed that it was precisely the willingness to be proven false, the critical mindset of being open to the possibility that you're wrong, that makes for progress toward truth.
   What scientists do in designing experiments that test their theories is create conditions under which their theory might be proven false. When a theory passes a sufficient number of such tests, the scientific community starts taking it seriously, and ultimately as plausible.