> but this is just plucking numbers out of the air.
It doesn't have to be. You can learn to give estimations of the "there's a 90 % chance this will be done before date X" and then when you look back at your 50 last projects, roughly 45 of them indeed were done before your estimated 90th percentile point.
Granted, the process will still look like plucking numbers out of the air, but the result will be more meaningful for planning than numbers actually plucked out of the air.
It doesn't have to be. You can learn to give estimations of the "there's a 90 % chance this will be done before date X" and then when you look back at your 50 last projects, roughly 45 of them indeed were done before your estimated 90th percentile point.
Granted, the process will still look like plucking numbers out of the air, but the result will be more meaningful for planning than numbers actually plucked out of the air.