How optimistic can someone be?: The Sydney Opera House is one of the most iconic examples of modern architecture in the world. Before construction started, it was estimated that it would cost around $7 million. Q: Can you guess what the final cost amounted to? A: $102 million! And the building took an additional 10 years to complete! If historical analogies hold, I am prepared to bet good money that pharaoh Cheops died of a heart attack when he saw the final bill for his pyramid … J

The planning fallacy: The above example is a perfect example of what is known as ‘the planning fallacy’. The idea is that we almost always underestimate how long it will take us to finish something – and how much it is going to cost. This is not a small effect – we are talking about huge discrepancies.

In a seminal study on this (watch this clip:, college seniors were asked to estimate how long it would take them to complete their honours theses. They were also asked to think about best-case and worst-case scenarios. On average, the students thought the task would take them at best 27 and at worst 49 days; on average, they calculated it would take them about 34 days to complete the work. In actual fact, it took them 56 days – almost twice as long! Only a handful among them managed to finish within the best-case time framework (Buehler et al, 1994).

The same results have been found in study after study. In another variation, students were asked to estimate with a 99% certainty how much time it would take them to complete a project. Only 45% of the students managed to meet the deadlines they had set themselves (Buehler et al, 1995).

The planning fallacy is partly an inability to factor in complexity; it is often impossible to calculate the impact that small obstacles or distractions may have on our ability to stick to our schedule. Another contributing factor is what psychologists call ‘the optimism bias’; it seems we have evolved to be over-optimistic about our abilities and our level of control over circumstances (see Sharot, 2012 on this topic).

The moral: In our field we do not have to worry about costs so much, but time is a different matter. The lesson to be gleaned from all the above is that things take longer than we expect, and big things (such as school plays, projects, dissertations, etc.) take longer still. Large organisations are well aware of this phenomenon, so when given estimates they make the necessary adjustments upwards. We could certainly learn something from them.

When planning, it would certainly help if we took past performance into account (‘How long did last years’ students need?’). Because students are not likely to do that, however, when it comes to long-term projects we need to help them by: i) breaking down a long process into stages; ii) setting deadlines for each of these; iii) being firm with these deadlines; iv) supporting students along the way by helping them prioritise their decision-making; very often it is perceived complexity that leads to paralysis.

Of fallacies and optical illusions:
It is important to note at this point that knowledge of this fallacy (and of a number of other similar biases) does not mean that one is insulated against it.

The fallacy is like an optical illusion; we know full well that lines (a) and (b) below are of equal length, but our eyes cannot help but see things differently. As Hofstadter’s law famously puts it: ‘It always takes longer than you expect, even if you take Hofstadter’s law into account!’ (Chabris & Simons, 2010: 125).

Principle: We tend to be overoptimistic about the time and resources it will take to complete something. The take-away: Factor in excessive optimism, use chunking and keep students to deadlines.



Baumeister R & Tierney J (2012) Willpower. London: Allen Lane.

Buehler R, Griffin D & Ross M (1994) Exploring the ‘planning fallacy’: Why people underestimate their task completion times. Journal of Personality and Social Psychology 67 (3) 366–381.

Buehler R, Griffin D & Ross M (1995) It’s about time: optimistic predictions in work and love. European Review of Social Psychology 6 (1) 1–32.

Chabris C & Simons D (2010) The Invisible Gorilla. London: Harper Collins.

Epley N (2014) Mindwise. London: Allen Lane.

Sharot T (2012) The Optimism Bias. London: Robinson.

Nick Michelioudakis (B. Econ., Dip. RSA, MSc [TEFL]) has been active in ELT for many years as a teacher, examiner and teacher trainer and he has given presentations in numerous countries.

He has written extensively on Methodology, though he is better known for his ‘Psychology and ELT’ articles in which he draws on insights from such disciplines as Marketing, Management and Social Psychology. For articles or worksheets of his, you can visit his blog at