WHY USE DNA?

Someone writes:

Wow, I just solved a 121-year old missing person case!I couldn’t figure out why a genetic match was a 2nd cousin in 23andMe and Ancestry when I know who all my 2nd cousins are. Building a tree for her, I found a surname that looked right but all other details were off. After testing a few theories, it turns out her grandfather was my long lost great-great uncle who left home at age 23 after an argument with his father in 1899 and was never heard from again. He changed his name, got married, and had kids and grandkids. Turns out that his draft registration and obituary listed the correct birthdate, birth mother, and even the birth neighborhood in England. Further email correspondence shows he told his wife details about his family (except for the right surname) that match exactly, right down to his father’s employer during the Civil War and his avid stamp collecting hobby. My new cousins were so frustrated to have a brick wall due to the wrong name. I would never have cracked it without DNA. I wish I could have told my late father.