Why does Superman wear underwear outside? (brain teaser)

Wearing underwear outside is a safety requirement in flight. Superman performs a high-risk and very urgent task, because Superman's coat easily enters the air during the flight, which affects the flight speed and safety. Underwear is much narrower than coat. Wearing it outside can wrap the coat more tightly, and fighting with bad guys will not get in the way. This example is like leggings for people marching. Of course, another important reason is that superman needs to have superhuman qualities! The author deliberately designed it to attract the audience's attention and improve Superman's influence.