I used to build model airplanes by the squadron -- the ones that came on big plastic "trees" that had to be glued together with model cement. I built and painted these planes with more enthusiasm than skill. When I took my time and followed all the instructions, the final result would look more or less like the illustration on the box. But all too frequently I'd be in such a hurry to get the thing finished that somewhere along the line I would skip a step (the old-school airplane glue didn't exactly sharpen my thinking in these situations either). Many times I found myself stuck with a model that didn't resemble the original because some piece or other was missing, backwards, upside-down, you name it. I've had similar problems over the years with do-it-yourself furniture, including one TV stand currently serving light duty as a supply shelf because I don't trust it to actually hold a TV.
Marketing campaigns are prone to the same trouble. If your print advertising conveys a different message than your website, and your website conveys a different message than your radio spot, and so on and so forth, you can't possibly hope to marshall the power that comes from a unified brand effort.
The word I'm looking for here is congruence. Congruence is a state of agreement. Behavioral scientists describe it as a state of internal and external consistency, with actions and appearances aligned with inner values and intentions. Consistent behaviors and actions allow you to make powerful statements and bring people around to your point of view. If, on the other hand, you speak with confidence but your handshake feels like a dead fish, that inconsistency weakens the power of your overall impression. The overall strategy may be intact, but some of the pieces are out of place or working at cross purposes.
That's why you must aim for consistency of tone and message across all your marketing channels -- website, blog, direct mail, social media, the works. Ideally, each piece of your marketing structure supports every other piece so that moving from one channel to the next feels natural and inevitable to the reader. Everything must work together to convey the same overall message, from the color of your business cards to the wording on your LinkedIn profile. All of your marketing content must display a consistent tone, attitude, and message. That's congruent marketing.
Strong, consistent messaging builds your brand and inspires confidence. Little inconsistencies are like cracks in the facade, weakening and eroding your brand-castle until visitors hesitate to venture inside. In the worst case, your brand becomes so all over the place that it ceases to be a brand at all. And then you have to start over. So check to see if your marketing structure has a few pieces missing or out of place -- and fix it (or hire a freelance copywriter to fix it for you) before the glue sets!