When I was a kid I got obsessed with Linux, but my family only had one PC in the living room. After an attempt to set up Windows/Linux dual boot where I messed up the partition table, my parents banned me from tinkering with it. Luckily I discovered Knoppix and other live distros, which allowed me to boot into a safe environment to play around in.
Knoppix LiveCD in 2004 was my very first try at Linux. The fear of HDD partitioning my parents' PC delayed me from installing Ubuntu Warty by a few months.
I remember also hosing the bootloader somehow on my first try of Linux, luckily my personal desktop so no collatoral damage!
After that I always had a CD wallet thing with copies of sysresccd and supergrubdisk and others (including I think an old knoppix cd from a linux magazine).