Within the first year or so of having installed Linux (mid-90's), I made the mistake of accidentally deleting /etc (wrote a script to tidy /tmp at boot, but it hadn't cd'd correctly).

That was possibly the best unix/linux learning experience of my life. Rebuilding /etc sufficient to rescue my files I cared about before a reinstall. Rescue CDs weren't really a thing, USB was a new thing at the time, and I was on dial-up.