In Azerbaijani we don't say "you are not important person", instead we say "adın it dəftərində yoxdur"; which literally means "your name isn't on the dogs' notebook".

This saying comes from Mongol era, when Möngke Khagan ordered empirewide census, in which every subject was counted, plus their belongings. In Caucasus and Iran, this task was entrusted to Arghun Aqa ( https://en.wikipedia.org/wiki/Arghun_Aqa ). His job was pretty hard and he was a harsh person.

So he made devters (in Mongolian, meaning notebook, same as dəftər in Azeri), where would be a list of subject names and their belongings. Women, elderly men and children wasn't in these devters. Turks called these devters as "Tat devters". Tat means "an Iranian or non-Turk".

So, if you were not in these "Tat devters" you were not important person, either disabled, very old, woman or child. This expression went through time and with a bit of vowel harmony, "tat" became "it".