Link Building vs Link earning, what is more useful in SEO?

Link building is what you make within your posts or to other posts in your blog. They are very useful for a visitor for easy navigation between the pages and one more thing, more the internal links more will be the page views. Research says that 80% of the visitors to a blog or website search for clickable links and they are more interested in clicking them. So, internal link building plays a major role in raising your page views and thereby increasing your earnings.
'Link earning,' is also a new term for me. But what I think is its a name given to paid links. Yes, if you write something i.e. a review of any product that is not yours you can earn links from the respective owner of product. Now you can build a link for the official product page i.e. external link. And you'll be paid for linking your page to theirs. This is how you earn by building links to other blogs/websites, called link earning.