One of the primary reasons for using agile software development (ASD) methods is to be agile – to deliver working software quickly. Unfortunately, this pressure often encourages ASD practitioners to make long-term trade-offs for short-term gains (i.e., to accumulate technical debt). Technical debt is a real and significant business challenge. Indeed, a recent study provides a conservative estimate of $361,000 of technical debt for every 100,000 lines of code. In this study, I examine the impact of the planning fallacy – people’s tendency to underestimate the time required to complete a project, even when they have considerable experience of past failures to live up to planned schedules – on the accumulation of technical debt in ASD projects. Using an experiment, I seek to establish a causal relationship between the planning fallacy and technical debt and to demonstrate that solutions to the planning fallacy can be leveraged to manage technical debt in ASD projects.