I know that this is a "mainstream" question, i don't want to know what to do if i get this message, i already know that there are so many topics about it, I would like to now "why", why can't i open two terminal windows and type-enter two differents "sudo apt-get install" commands? Why does ubuntu have to "lock" this folder?
If you run two instances of
apt-get install they will try to write to the same files that will cause conflicts.
That is why the system does not allow to do it.