Have you heard or used the above claims before?
Like many commonplaces in language and culture, you can trace these claims back to a philosophical source. Protagoras (pro-TAG-er-us) of Abdera, a contemporary of Socrates, is credited with the first formal statement and defense of these claims and is the first proponent of the philosophical view known today as relativism.
Protagoras wrote many works, the most important being Truth (Alethia) and On the Gods (Peritheon). Unfortunately, none of his works have survived the destructive forces of the ages (e.g. Library of Alexandria). What is known of Protagoras comes to us from the writings of other philosophers especially Plato, Aristotle, Diogenes Laertius, and Sextus Empiricus. This leaves us with just a few fragments of the great volume of work that Protagoras produced. Being that just a few surviving sentences have such influence on us, imagine how rich it would be to have his entire body of work.
Protagoras was a sophist. The sophists were self-proclaimed teachers who travelled the Greek cities offering to teach young men arts such as rhetoric and public speaking. These were extreemly useful skills in a quasi-democracy such as Athens, where the ability to persuade the majority could lead to political and economic power. Some sophists claimed to be able to teach knowledge, wisdom, and virtue, apparently on the basis that such qualities were defined by majority opinion (hence, if you can convince the majority that you are wise, then you are wise).