Why my pip installations requires python -m install --user?
The error basically states that you do not have permissions to write files to your machine, So ff you are a root user(or admin) you can always install python packages with 
sudo pip install django
Or 
pip install --user django
--user makes pip install packages in your home directory instead, which doesn't require any special privileges.
I am running this inside a virtual environment. 
When I type: 
pip install django 
I get:

ERROR: Could not install packages due to an EnvironmentError: [Errno
  13] Permission denied: /home/ENV/env/lib/python3.5/site-packages/pytz
  Consider using the --user option or check the permissions.

For it to work I actually need to input:
python -m pip install --user django 
Why?