Essentially, your brand promise encapsulates all your customers' expectations on what your company provides.

It's basically what people should expect when they do business with you.

It defines your company and guides every decision you make, every action that you take. Like ripples in the water.

This includes:

The product/service itself
How it is delivered
The customer service you provide
What you stand for
Even the feelings it evokes in them

A strong brand promise statement is able to convey all of this in a singular phrase. Here are examples of some of the world's most famous brands.

Apple: “Think different.”
BMW: “The Ultimate Driving Machine”
Geico: “15 minutes or less can save you 15% or more on car insurance.”
H&M: “More fashion choices that are good for people, the planet and your wallet.”
Marriott: “Quiet luxury. Crafted experiences. Intuitive service.”
Nike: “To bring inspiration and innovation to every athlete in the world.”
Starbucks: “To inspire and nurture the human spirit – one person, one cup and one neighborhood at a time.”
Walmart: “Save money. Live better.”

Some of these are also used as their taglines (e.g. BMW's Ultimate Driving Machine) while others are an internal mantra (e.g. Nike's “To bring inspiration and innovation to every athlete in the world.”). But what is similar in all of them is that they not only give you a clear sense of what they do, they also inspire people. They evoke a higher sense of purpose. When you read the words, you want to support them. Because they're not just about delivering a product. They show a vision of how things should be. Their unique point of view of the world.

Crafting a well-formed inspiring brand promise is not easy. But here's a process to help you get the essence.

Start with your ideal customers. What do they care about, in regards to your product?
Next, look inward. What do uniquely believe about what you do?
Then, look beyond. How does what you do make the world better? Yes, it sounds corny and overreaching. But really think about the positive difference you can genuinely make.
Finally, identify what you can promise that delivers on all of these things.

You can use this worksheet to help you get started.
Download Brand Promise Worksheet

Now, after you've filled all of that out, you still don’t have a finalized brand promise. To get something like "Think different" you need to continue to refine it. But this should provide you with a solid frame work to start.