Penetration testing is the art of finding an open door. It is not a science as science depends on falsifiable hypotheses. The most penetration testing can hope for is to be the science of insecurity - not the science of security nasmuch as penetration testing can at most prove insecurity by falsifying the hypothesis that any system, network, or application is secure. To be a science of security would require falsifiable hypotheses that any given system, network, or application was insecure, something that could only be done if the number of potential insecurities were known and enumerated such that the penetration tester could thereby falsify (test) a known-to-be-complete list of vulnerabilities claimed to not be present. Because the list of potential insecurities is unknowable and hence unenumerable, no penetration tester can prove security, just as no doctor can prove that you are without occult disease. Putting it as Picasso did, "Art is a lie that shows the truth" and security by penetration testing is a lie in that on a good day can show the truth. These incompleteness and proof-by-demonstration characteristics of penetration testing ensure that it remains an art so long as high rates of technical advance remains brisk and hence enumeration of vulnerabilities an impossibility. Brisk technical advance equals productivity growth and thereby wealth creation, so it is forbidden to long for a day when penetration testing could achieve the status of science.