popularity, reputation or authority. Others rely on personal intuition.
Without a universal theory and with lessons learned from experience that cannot be generalized and with lack of profs, the answers we have to many questions from the day-to-day work are not always correct. Some are based on wrong assumptions, some have been over-generalized and some have not been properly verified.
By one side there are the IT industry and practitioners, on the other are researchers and academics. There is a near-complete disconnect between the two [1]. And it doesn't help.
Socrates:
It is likely that neither of us knows anything worthwhile, but he thinks he knows something when he does not, whereas when I do not know, neither do I think I know; so I am likely to be wiser than he to this small extent, that I do not think I know what I do not know