When you don't know what a pregnant woman is, you won't notice that many women around you are pregnant. Once you understand the concept, you'll often see pregnant women. The world changes based on personal perception; it's not that there are more pregnant women, but that perception has changed.
Psychologists can always find people with various psychological problems around them, and it's the same reasoning.
Qian looked at the people under the overpass. How many of them have severe psychological illnesses like Zheng Xu?
Very few.
But how many people need psychological counseling or are in a bad mood?
Many.
Everyone will have things that upset them and moments of bad mood; it's just that many problems can self-resolve over time.
