In the process of trying to plan better, I realize that I end up underestimating the amount of time that it takes me to do something, and overestimating what I can get done in a given period of time.
From talking to friends and colleagues, this appears to be a common observation, including by people who we might consider as successful.
The name for this is Hoftstadter’s law, or the planning fallacy. We tend to consistently blow past not only our best case scenarios for how long things take, but also our worst case scenarios.
What’s the solution? One option is to try a ‘premortem’. Assume things have already gone wrong and you missed your deadline. Ask yourself what happened and what went wrong, and then plan accordingly.