Not too long ago, I compared your marketing campaign to the human brain. While other business components - from your website to sales representatives - compose different organs, the brain is what makes everything function the way it should.
Another apt analogy would be that online marketing is really like cooking, where you need the right amount of each ingredient, and if you don't have all of the ingredients the outcome can be quite disappointing.
Keywords: The "butter" of online marketing
If you're a baker, then pretty much everything you make includes butter at one step or another.