Not tracking Wizard down when Diggy lost MetroRP when his computer died back in 2011. Backstory: Wizard was hosting MetroRP at the time, therefore had the only copy of the mod. Sure, I did end up tracking Wizard down in 2014, but it was really too late by then.
And if you want some spy kid info on how I managed to track Wizard down, I googled their AIM username, which linked to a forum profile on a different website, which then had a section listing people who visit that profile, which then had a profile with a username very similar to Wizard and bingo. Also, not possible to do now since AIM doesn't exist anymore and that stuff isn't displayed.