Just because you're good at X doesn't mean you're good at every (X, a) composition. For example, being a good golfer doesn't imply you'll be able to teach it; being a good singer doesn't imply you'll be able to write music; and being a good domain expert doesn't imply you'll be able to recognize a design that most effectively causes customers to purchase the products/services in your domain.
The comic said: "The client has completely forgotten that they hired you, the web designer, to build them a great product."
Whereas I see: "You have forgotten that the client is paying you to build a site which best represents the business in which they are the domain expert."