[deepstack]

>How would you react if someone came in and said "there is no real gravity; it's just that the earth loves us very much"? Or "there are no viruses and bacteria; we get sick from bad air and evil spirits"?

Gravity can be measured more objectively than social science (such as psychology) concept such as introvert/extrovert, which is determined by committees such as DSM IV or maybe now V. Introversion and extraversion are just one thing that is measured within a certain context.