So you, as an SEO, take on a new project for a client who wishes to boost his rank. Say his business is auto mechanics.
In order to write good content, it is essential integral to have good knowledge on the subject at hand.
Withouth backlinks the site will not rank. To build backlinks, one must take part in writing guest blogs, blogs on own site, forum interactions etc. etc. - how can you confidently interact with people in that community without the knowledge of mechanics?
Same thing with social media - Yes, its all great have 2000 followers/likes - but again if a question is asked on the facebook page - do you get the client to answer? How does it work?