This article was originally published on Forbes.com.

Creating happy clients and customers is the key to growing your business. Happy customers are loyal customers, and they become the most powerful promoters of your business when they spread the word to their network. So, how do you make (and keep) your customers happy?

For all of the thousands of books that have been written about happiness and how to find happiness in life, in my experience, it comes down to a simple formula: Happiness = reality – expectations.

In any given situation — whether it’s a relationship, vacation, book, etc. — your happiness is dictated by the reality of the situation stacked up against your expectations.

If you expect a movie to be OK, and it turns out to be great, you’re happy. But if you expect a movie to be great, and it’s really just OK, you’re disappointed. It’s not the reality of the situation that creates happiness, it’s the reality compared to the expectation.

Expectation management is key in order to create happy clients who give you referrals. This can be a challenge and sometimes even a point of contention between your operations team and your marketing and sales teams. Your marketing team wants to make the biggest, boldest promises possible in order to make a sale. But if they make promises that your operations can’t live up to, you end up with disappointed customers.

So, to maximize referrals — and for the long-term health of your business — it’s important to manage expectations carefully. For example:

Define and limit the ‘results’ your marketing and sales can promise.

If your product or service takes six months to create noticeable results, your sales team shouldn’t be telling people that it will happen in three months. As an example, in my business, it takes us about 60-90 days to build and launch a new website. But we once had a salesperson telling clients that we could probably get their site done in 30 days. Inevitably, we didn’t live up to that promise. Lesson learned: Script and enforce the promises our sales team can make.

Underpromise and overdeliver.

It’s a pet peeve of mine when somebody tells me that something will take two days and then it takes a week. When making a time commitment to someone, always give yourself room to beat the timeframe you committed to, or at the very least, meet it. If it’s going to take you one day, tell them it’s going to take two. Then, when you beat that timeline, they’re thrilled.

This is an easy opportunity to exceed expectations, yet for whatever reason, most people over-promise and then can’t deliver, creating unnecessary negativity and disappointment.

Look for opportunities to create ‘wow’ moments.

The cliche here is to always go the extra mile for your clients and customers. But that’s not always realistic. And honestly, it’s not smart. Good enough is good enough. (Note that “good enough” looks very different depending on who your customers are and what they’re paying you.)

However, even within the real-world time constraints that you and your team have to face, you can find time to strategically go above and beyond to create a “wow” moment for a client. For example, when a customer or client asks for help that goes beyond your scope, don’t just apologize and say you don’t do that. Take a few moments to find somebody else who can help them, and point them in that direction. If possible, throw in a few words of advice and perspective to help them out.   

Tell the truth, do what you say you’re going to do and look for opportunities to surprise and delight your clients. None of this is revolutionary. In fact, it should be common sense. Yet, I’m constantly surprised by how often businesses fail to meet these basic expectations.

The good news is that if you and your team can communicate well, act with integrity and generally get the job done right, you stand out in a sea of mediocrity. Focus on the fundamentals. Manage the expectations of your customers and clients carefully and strategically. If you do this consistently, you’ll have loyal customers and raving fans of your business. And that is the formula for real, rapid and sustainable business growth.