Leadership author Daniel Pink gave props to the book "Instant Influence: How to Get Anyone to Do Anything - Fast!," by Michael Pantalon, for its helpful advice on this perennial conundrum.
On his blog, Pink quotes the following tip:
"Imagine you're a manager at a major PR firm and one of your reports balks at revising an important part of the next big campaign. Instead of asking rational but ineffective questions, try the following two seemingly irrational questions:
1. How ready are you to make the revisions, on a scale from 1 to 10, where 1 means not ready at all and 10 means totally ready?
"On the rare chance that she says, '1,' surprise her by saying, 'What would turn it into a 2?' In telling you what it would take for her to become a 2, she reveals what she needs to do before she is able to make the revisions to the campaign. That is what you motivate her to do first."
2. If she picks a number higher than 2, ask, 'Why didn't you pick a lower (yes, lower) number?'
"Question 1 seems irrational, because you're asking, 'How ready are you...?' of a person who just said, 'No,' which we can assume means not at all ready. However, most resistant people have some motivation that they keep from us.
"If you ask, 'Are you going to take my suggestion, yes or no?' they continue to keep their motivation hidden. But if you ask them the '1-10' question, they're much more likely to reveal their motivation by saying a 2 or a 3, which is far better - you've now moved from a 'No' to at least a 'Maybe.'
"Question 2 seems really irrational, perhaps even absurd... However, by asking Question 2, you're asking her to defend why your directive to revise the campaign is even the slightest bit important to her... rather than to defend her excuses why she won't do it (e.g., too busy).
The answers she gives lead her to rehearse the positive and intrinsic reasons for doing what you asked, which, in turn, dramatically increase the chances that she gets the project done."