diff --git a/19-Objective-Personality-Testing.Rmd b/19-Objective-Personality-Testing.Rmd
index 5b299c25..b2d3cde8 100644
--- a/19-Objective-Personality-Testing.Rmd
+++ b/19-Objective-Personality-Testing.Rmd
@@ -423,6 +423,7 @@ Ways to improve self-assessment are described by @Dunning2004:\index{self-report
 - Introduce "desirable difficulties" to instruction, such as spreading training over several sessions and varying the circumstances of the training.\index{self-report!ways to improve}
 These challenges can harm the speed that students learn but leaves them better able to retain what they learned and to transfer it to new situations in the future.\index{self-report!ways to improve}
 - To account for over-confidence, add in safety factors and buffer time.\index{self-report!ways to improve}\index{over-confidence}
+People tend to under-estimate how long it will take to complete a project, known as the planning fallacy [@Kahneman2011].\index{self-report!ways to improve}
 For instance, add 30%–50% extra time to all time-completion estimates for projects.\index{self-report!ways to improve}\index{over-confidence}
 
 ### Satisficing (Versus Optimizing) {#satisficing}