Imaginary work is always easier to do than real work. It is much more attractive (being more quickly done) and once you see the imaginary work, it can be very difficult to identify the real work it masks. People estimating imaginary work often assume they have all the facts in hand when making their estimates, which assumption leads them to believe that there is no “big technical hurdle” preventing its implementation.

Jamis Buck, programmer for 37signals, on the public's tendency to underestimate the time and effort required to develop even the "simplest" features. (Via Gruber.) (#)