>>165
Off the top of my head:
/bin - system binaries for single-user mode
/dev - devices
/etc - system configuration files
/usr/bin - system binaries
/usr/lib - system libraries
/usr/share - read-only system program data
/usr/local/bin - application binaries
/usr/local/lib - application libraries
/usr/local/share - read-only application data
/home - user directories

If it takes you "hundreds of valuable hours" to remember the above, you have issues.