When I was 12, I had a crush on a slightly older girl. I was shy and never could think of anything to say to her and, before I knew it, she was gone. I didn't know her name, didn't know anyone who knew her - there was no way to find her again.
It was the first time I'd encountered a seemingly impossible but solvable problem. She existed, therefore she could be found; I just had no way to do it. I've spent my life solving other similarly "impossible" problems and I'd think of her for maybe a minute every five years.
Yesterday, I solved the problem. Though I lived in a city of a million people when I was 12, the world of my acquaintance was much smaller. She would undoubtedly have gone on a few years later to attend one of six high schools in the area. High school yearbooks are available, so all I had to do was look through 2000 photos. An hour later, I found a photo of her at age 16; time had altered my memory of what she looked like, but it was undoubtedly her.
Now I had a name, an age and a home town for her, so I could do either an internet search or an old-fashioned document search to find her. I chose not to. I'd rather remember her as a pretty 13 year-old with her future ahead of her. The point was that I could do it if I wanted to. It's undoubtedly a major character flaw that I won't let something be over until I say it's over, but I did solve the problem and it only took 38 years.
Now I can say: When I was 12, I was in love with a pretty girl. Her name was... Lynda.