The comic, however snarky and cute, manages only to obscure the point further. The (E) [in the comic] is different than other ones, because there's no exchange of goods nor services for the money between the company and its owner, the Shareholder.

Let me put it my way:

When a plumber puts his knowledge and tools to work, his revenue is taxed once, at personal level.

When a shareholder puts his knowledge and money to work (along with other shareholders, in form of a company), his revenue is taxed at both company level and again at private level.

Can you spot the double taxation now?