Does flexibility help or hurt in dealing with others? Last week’s Republican debate featured a vigorous discussion of the issue. Trump sang the praises of flexibility, saying, “I’ve never seen a successful person who wasn’t flexible and who didn’t have a certain degree of flexibility.” Rubio noted the drawbacks, suggesting that Trump was so flexible he should do some yoga moves. Who’s right?

Sorry to say that negotiation research indicates it’s much more complicated than the politicians make it out to be. In particular, research suggests that flexibility is helpful in some circumstances and harmful in others. Thus, although this is not a blog about politics, I thought this might be another appropriate time to wade into the national discussion. So what does research have to say on when to be flexible?

1. When you’re talking about means rather than ends. You go into a negotiation to achieve specific ends, often called your interests. The tactics you use to achieve those interests are your means. Rubio is right that flip-flopping on your core interests amounts to wimpiness. But Trump is right that flexibility on how you get there—the kinds of means you consider—is often the only way to find any way there at all. The best negotiators are rigid on their interests but flexible on the possible pathways that lead them there.
2. When you’re talking about a relatively unimportant tissue. In any negotiation, some issues matter a great deal. You just have to find a house with better schools. Other issues are less essential. A fireplace would be nice but you could probably live without it. Rubio is right that flexibility on the critical issues is foolish. But Trump is right that rigidity on the unimportant issues is too. The best negotiators know how to flexibly trade their less important issues in order to stubbornly insist on their most important issues.
3. When the facts change. Sometimes, the world frustratingly changes its mind in the middle of the negotiation. Your salary bump isn’t quite as big as expected—and as needed to afford that big house. In a stable and unchanging world, Rubio is right that shifting positions is the mark of a wobbly leader. In the changing world we often encounter, however, Trump is right that leaders have to adapt. The best negotiators know how to hold firm in stable times but adapt as instability arises.
4. When your tastes change. Sometimes the world stays the same, but it’s you that changes your mind. Perhaps you thought you could deal with that split-level floorplan, but you’re now thinking it would make you nauseous each time you open the door. Rubio is right that the leader of the free world shouldn’t let their tastes shift whimsically with the wind. But Trump is right that real people do change their minds. The best negotiators know how to establish firm preferences but change their positions if their preferences happen to meander.
5. When you realize you’ve made a mistake. Sometimes, you realize you made a big flippin’ error. Your initial decision was just downright wrong. You didn’t look hard enough at the school data; now that you do, you know you can’t buy this house. Rubio was right that the president can’t afford too many judgment errors. But Trump was right that holding firm in the face of an error is foolhardy. (In fact, it’s a documented decision bias called escalation of commitment.) The best negotiators know how to make and stick to the best decisions but also admit their errors and flexibly move on.

I wish that the truth about flexibility was as simple as a soundbite about small hands. But the world doesn’t care what I wish, and we’ve heard more than enough about hand size anyway. So the best leaders can only use their best judgment about the situations they face, trying to determine whether those situations call for enlightened flexibility or firm intransigence.