In software, until we acknowledge the way in which the coastline paradox[0] pertains to task estimation, we're going to continue spinning our wheels saying things like "people have worked on this area before, the estimation should be easy" and keep getting really inaccurate estimates, and the engineers will continue to be blamed.
The fractal nature of task complexity suggests that _complexity can only go up_ (more or less). This is why estimates always seem to be wrong in the direction of "too short".
Your comment about hole digging is to assert that the fractal dimension[0 again] is 1 for that particular problem. Great! Estimation is easy in those cases.
My proposal: identify the particular fractal dimension of your particular problem domain (by observing past estimations compared with their reality) and use it as a multiplicative factor in estimates.
Unfortunately, most managers call this process "sandbagging" and my proposal is considered too "mathematically complex". I believe that until this is accepted and resolved, we will continue to have unrealistic estimates.