Planning Fallacy

The underestimation of the time needed to complete a project or programme of works.

There are many variables which can impact on a planned programme of works:
• especially by being too optimistic on the timings;
• the impact of external factors – for example the weather, supply issues, reliance on external contractors;
• less efficient machinery or machinery breakdowns and malfunctions;
• changing staff motivations or availability due to illness, holidays, staff leaving employment;
• new training requirements, skills of newly recruited staff, abilities of agency staff;
• tiredness, being over-worked;
• predictions made from previous activities, but which had significant hidden differences in the detail of the programme;
• as well as not fully understanding what is required to achieve to undertake and complete the required project.
(See also Roger Buehler, Dale Griffin, and Michael Ross, (1994) , ‘Exploring the "Planning Fallacy": Why People Underestimate Their Task Completion Times’, Journal of Personality and Social Psychology 1994, Vol. 67, No. 3.366-381, accessed 2nd December 2023)