Many people think that getting someone to say “yes” is about persuasion, making the perfect argument, choosing the right words, or asking nicely.

But decades of research suggest something counterintuitive: One of the most reliable ways to get to a “yes,” is to give the other person permission to say “no.”

Studies have shown that across all kinds of situations, from marketing to negotiations to everyday requests, simply adding a line like, “but you are free to accept or refuse,” makes people far more likely to comply.

It taps into one of our deepest psychological needs: autonomy. When people feel pressured, they resist. But when they feel they have a choice, they tend to engage more willingly and push back less.

I’ve spent the past decade advising Fortune 500 companies as an educator and behavioral researcher, and I’ve seen this principle outperform the hard-sell. Here are four simple phrases you can use to put this principle into practice.