@thegibson there isn't a character limit high enough in the world to capture my failures. Here's a crucible moment though, from my first or second year in the business:

Working at a regional ISP in the 90s. I zeroed out /etc/passwd on the mail server. predated virtual users so every customer had a system account. Thought I had a) lost my job and b) killed the business. Boss said to me, "Well, now you're a real sysadmin. Go get the install CDs."