Over the past years, two trends have emerged in consumer businesses. Now, they are colliding.

The first trend is the improvement in marketing science, expertise, and accountability. Modern developments have seen marketing transformed from a “colouring-in department” to the engine of business growth. Today the marketing discipline includes psychologists, data analysts, digital architects, researchers, actuaries, and scientists, in addition to the traditional roles of the past.

As a result, marketing has improved. Marketers have left “gut instinct” behind and replaced it with evidence-based strategies that lead to campaigns crafted from genuine insights.

The second trend is improved business efficiency. Business leaders have become quite proficient in cutting costs from their operations. Mergers and acquisitions, modern procurement, process streamlining, new technologies, vertical integration, and supply-chain optimisation have lowered costs and increased profits.

You would think the combination of these two trends would lead to record volumes and profits. And, in many cases, they have. But now they can also lead to disaster.

A few weeks ago, seeking a quick lunch, I walked along a busy street where three fast-food (they prefer to say “quick-service”) restaurants were located side by side. All three are global brands selling burgers, chicken, and the like.

As I approached the first one, I met a man coming out of the restaurant. He had a scowl on his face. As I reached for the door he offered me some advice: “Good luck,” he said, “it’s a shit-fight in there!” He was right. The place was crowded with customers, all trying to line up to be served at the counter. I would guess there were about 20 to 30 waiting to be served (it was lunch time, after all). Trash was overflowing the bins. Exasperated mothers pleaded with children to stop running about. People checked their watches, rolled their eyes, and texted news of their tardiness. Behind the counter, I could see two employees. Two. I suspect another was out of sight, perhaps hiding from the angry mob!

I followed the example of the man who had given me the early warning and left. There were, I thought to myself, two other choices just steps away. I visited both and was greeted with nearly identical experiences. I skipped lunch.

I believe I was witnessing the “trends collision” firsthand. Marketing had done its job. Customers had decided to spend their money with those establishments. No doubt they had been convinced that they would receive a tasty meal, at a good price, in a clean building, served quickly by friendly employees. That would have been the promise. On this day, that promise was broken.

Why? It appeared to me all three restaurants were significantly understaffed. The efficiency trend had gone too far. In this case, cost-cutting has resulted in an inability to deliver the fundamental service promised by marketing. Cost-cutting can be a bit like trimming a sausage. You can make a smaller and smaller sausage in this manner. But at some point, you no longer have a sausage.

These colliding trends are not reserved to fast-food restaurants. I’m sure you see it everywhere. Airlines, retail, banking, and others have been cutting costs and breaking promises.

The greatest danger, I propose, is not slow service — it’s the broken promise. People will wait patiently for an espresso, because no one promised they’d get it in 20 seconds. You are not angry if it takes one hour to fly from A to B. You are angry if they promised to get you there in 30 minutes.

So what are you promising your customers? Accurate news stories? Prompt delivery of a newspaper? Updated Web sites? Complete coverage of sports? If those promises are motivating and relevant, then you have two choices: Work to make sure the promise is delivered. Or change the promise.

People can be very forgiving. But most hate being deceived. Or having a promise made by a brand they respect and then having it broken.