Yes, it's an abstract and subjective thing, but on average we know what is.  For example, have commandline as unique option for restart or shutdown the computer is not a common-people-friendly way. ed, sam or acme to edit a simple text file wouldn't be friendly if the user were my mom: maybe notepad would be a better choice for her. Browse by the directory tree with the cd command isn't friendly for them too: perhaps a traditional file manager with a list of directories in a column in left and selected directory content on the right would be better.