I was born here in the United States and as a Korean-American, the logic is this. What doesn't harm me doesn't need to be considered a big deal. It is pretty crazy. I used to ride bikes in pouring rain and walk in the rain as well and the reason behind that is "Eh it is just water I am going to take a hot shower afterwards so no problem." Also, it is "Oh, I forgot my hat oh well." Now where I live it sometimes pours like "cats and dogs" and when that happens I run as fast as I can to the car and laugh at myself for getting wet. I think it is just how we are grown up here. Getting wet is no big deal and what doesn't kill us makes us stronger is a strong mentality here in the States. Also, it is a pain opening the umbrella and closing too. We don't think it is worth the hassle. So, to answer your question, my Korean friend, for me the answer is "I am just lazy" lol. 😊