As salespeople, we are driven to say yes – “Yes, we can rush your order to you by the end of the week;” ”Yes, I can get you that 5 percent discount;” ”Yes, I can be there an hour earlier.” Why are we so eager to be agreeable? Simple: we assume a “yes” will make a customer happy and that a happy customer will buy from us.

The problem is that we often say yes when we should say no because we don’t know how to say no in a way that doesn’t put off and offend others. When we learn how to use no correctly, says William Ury, director of the Global Negotiation Project at Harvard University, “this one word has the power to profoundly transform our lives for the better.”

In his book, The Power of a Positive No (Bantam, 2007), Ury explains how to say a positive no using a “yes, no, yes” statement. For instance, say you’ve been working long hours for several weeks and on the one night you and your spouse have planned to have dinner together, a local community organization calls and asks you to speak. It’s an important group and you’d like to keep the door open for a future engagement. Your “yes, no, yes” statement might sound like this, says Ury: “It is good to hear from you and good to hear of all the valuable work the center is doing. For family reasons, I am not taking on any additional commitments at the time. Next year, if you are still interested, I’d be happy to consider it. Thank you for thinking of me.”

See? You’ve said no, but by bookending it with two yeses – two positive statements – you have strengthened the relationship and made it easy for the other person to accept your no. Here’s a closer look at the yes-no-yes formula:

Yes #1: This is the underlying purpose for which you are saying no. In the example above, it was “for family reasons.” For a customer who keeps asking you to jump through hoops to meet with him, it might be “due to my commitments to other customers” that you can’t move your schedule around. For a customer who keeps demanding price reductions, your underlying purpose in saying no might be fairness to all your customers, or the fact that further reductions would jeopardize your company’s financial stability. Ask yourself: what am I truly standing up for? What overriding value or need am I protecting? Uncovering these answers, says Ury, “grounds you in something positive and gives you a sense of direction.”

No. The more dependent you are on the other person, the more power you give them and the less likely you are to be able to say a confident no. Thus, Ury advises you to come up with a solid Plan B before you say no. Plan B is an action you can take independent of the other’s cooperation. For instance, if you’re saying no to a customer who keeps pressing you with unreasonable demands, your Plan B might be to find a new customer or to involve your boss, who can contact your customer’s boss to see if they can work it out. A Plan B is crucial because it gives you positive power to meet your own interests. “It is not always easy to say no, particularly to people on whom we depend,” admits Ury. But having a solid backup plan gives us the confidence to do it.

Yes #2: Your final statement prepares the other person to say yes to your no. In other words, you need to “open a channel of communication that makes it possible for the other person to hear and understand your no as essentially positive,” says Ury. The key: respect. By truly respecting and listening to the other person, you open the door to their mind. For instance, in turning down the opportunity to speak, the statement, “Next year, if you are still interested, I’d be happy to consider it,” leaves the exchange on a positive note.

In essence, the first yes expresses your interests, the no asserts your power, and the second yes furthers your relationship. The first yes is internally focused, the second, externally focused. “A positive no thus balances power and relationship in the service of your interests,” concludes Ury. It takes practice, but the rewards, when you get it right, are significant.