  Delays in activities completion drive human projects to schedule and cost
overruns. It is believed activity delays are the consequence of multiple
idiosyncrasies without specific patterns or rules. Here we show that is not the
case. Using data for 180 construction project schedules, we demonstrate that
activity delays satisfy a universal model that we call the law of activity
delays. After we correct for delay risk factors, what remains follows a
log-normal distribution.
