A handy technique I found was that whenever a programmer balked at giving an estimate, I’d ask, “What questions can I answer that would make you more confident about giving an estimate?” By getting him to be specific, I gave him the opportunity to confront the fear or frustration he might feel, which allowed me to help solve his problem.

Making Things Happen, Scott Berkun

Found this passage to be quite enlightening, and I have got to remember to use it if the case presents itself!