At first sight, you might say that the line at the top is longer. But in fact, both lines are the same length. The feather-tailed (羽毛尾的) line (above) just appears to be longer than the arrow-headed (箭头形的) line. German sociologist Muller-Lyer discovered this phenomenon (现象) in 1889 and named it the “Muller-Lyer illusion (缪氏错觉)”. Last semester, I learned about it in my psychology class. After learning about it, we were asked to explain why people are fooled by this illusion.