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!