Emotional tears have been considered honest and sincere signals, most likely because they are difficult to shed on demand. At the same time, people acknowledge that tears can be strategically used to manipulate others - so-called crocodile tears.
The power of this feedback loop is one of the greatest insights of modern empirical psychology. It underlies stereotype research, mindset research, most of social psychology, and even the most-used form of talk therapy in the world (CBT).