December planning sessions are in full swing, and leadership teams across companies of all sizes are setting aggressive targets for the new year. Throughout my career, I have consistently seen savvy executives projecting 40% revenue growth, record-time product launches, and flawless execution.
Here is the uncomfortable truth: most of these plans are built on cognitive quicksand.
The Uncomfortable Reality of Business Planning
Psychologists Daniel Kahneman and Amos Tversky gave us the term for this phenomenon in 1979: the planning fallacy (Kahneman & Tversky, 1982). It describes our persistent tendency to underestimate the time, costs, and risks of future actions while simultaneously overestimating the benefits. In 2003, Kahneman and Dan Lovallo expanded this concept for business leaders, showing how this cognitive bias leads executives to make “overly optimistic forecasts” that doom initiatives to fall well short of expectations (Lovallo & Kahneman, 2003, p. 56).
The data is sobering. Research on thousands of major projects reveals that 91.5% miss their time or budget targets—or both (Flyvbjerg et al., 2003). Fewer than 1% deliver on time, on budget, and with expected benefits. Yet every December, leadership teams confidently plan as if they will be in that magical 1%.
Why Smart Leaders Fall Into This Trap
The planning fallacy is not about incompetence or laziness. It is hardwired into how we think, amplified by three powerful cognitive biases that turn reasonable forecasts into wishful thinking:
Optimism Bias: Entrepreneurs and executives are naturally optimistic—it is what gives us the courage to build companies. We genuinely believe we will beat the averages, overestimating success while underestimating setbacks (Sharot, 2011). During year-end planning, when everyone says “Yes, we can!” these rosy plans go unchallenged. Within organizations, individual biases become “mutually reinforcing,” validating unrealistic views (Kahneman, 2011).
The Availability Heuristic: We judge probability based on easily recalled examples. That quarter when your team hit 150% of quota? Vivid memory. The dozens of 85% quarters? Background noise. This causes us to base forecasts on memorable wins rather than statistical reality (Ariely, 2008). We recall the unicorn startup and forget the hundreds that folded.
Motivated Reasoning: Organizational pressures to set ambitious targets—to impress investors and boards or rally teams—lead us to unconsciously adjust assumptions to reach desired conclusions (Lovallo & Kahneman, 2003). “Stretch goal” culture can make pessimistic voices unwelcome.
The December Effect: When Holiday Spirit Meets Strategic Planning
Year-end planning creates a perfect storm for the planning fallacy. The New Year feels like a clean slate—a chance to finally get it right. Behavioral scientists note that optimism peaks when approaching symbolic milestones (Buehler et al., 1994). Surrounded by celebratory energy, teams imagine best-case scenarios while risks feel distant.
The result? Revenue forecasts resembling hockey sticks. A SaaS company predicts doubling its customer base by March, banking on zero churn and flawless execution. How often does everything go right?
The Real Cost of Unrealistic Planning
The planning fallacy has real consequences: credibility erosion when boards and investors brace for missed targets, resource misallocation when projects take 50% longer than planned, team burnout from unrealistic deadlines, and strategic misalignment when roadmaps constantly shift. As one CEO told me, “Our New Year’s goals often turn into April’s apologies.”
Building Reality-Based Roadmaps
Awareness is crucial, but what can you actually do during your December planning sessions? Here are four practical strategies I have seen work:
1. Adopt the Outside View: Before finalizing any major initiative, ask: “How long do similar projects typically take?” Ground your roadmap in base rates and historical data, not hopes. If only 1 in 10 product launches in your industry succeed in year one, acknowledge that reality (Kahneman, 2011). As Philip Tetlock and Dan Gardner demonstrate in Superforecasting (2015), the best forecasters systematically compare their predictions to historical base rates.
2. Run a Pre-Mortem: Imagine it is next December and your plan failed spectacularly. Have your team brainstorm why. This exercise, popularized by psychologist Gary Klein, flips the script and uncovers hidden risks while they are still cheap to address (Kahneman, 2011). It is easier to be realistic about a hypothetical failure than to be pessimistic about a hoped-for success.
3. Protect the Skeptics: Create a culture where raising concerns is not being “negative” but prudent. One characteristic of highly successful CEOs: they actively seek out the team member who will say, “Here is what could go wrong.” Reward those who speak up with inconvenient data—they are helping you avoid expensive mistakes.
4. Build in Buffer Time: Research shows we systematically underestimate how long tasks take, even when we know our past estimates were wrong (Buehler et al., 1994). For any major initiative, add 25-50% to your timeline estimate. It feels excessive in December; it will feel prescient in April.
A Challenge for Your Planning Session
As you head into the final 2025 strategy meetings, designate someone as the “Chief Realism Officer.” Their job: question optimistic assumptions, point out historical precedents, and ask, “What is our plan if this takes twice as long?”
It will not make you popular in the moment. However, when you are presenting Q2 results and hitting the targets you set, you will be glad you did.
The planning fallacy is not about killing ambition—it is about giving your bold vision the best chance of success by grounding it in reality. Your competitors are probably making 2026 plans right now, powered by holiday optimism and cognitive biases, setting themselves up to miss targets and erode credibility.
You can choose differently.
Rich Smith is an executive advisor, behavioral marketing strategist, investor, and CMO known for helping leaders finally understand not only what strategies work, but why. With three decades of experience leading growth across financial services, healthcare, technology, and consumer brands, Rich has guided companies through crises, rebuilt brands from the ground up, and helped position organizations for nine-figure exits. Connect with him on LinkedIn, at RichSmith’s.blog, and The Revenue Science Podcast.
References
Ariely, D. (2008). Predictably irrational: The hidden forces that shape our decisions. HarperCollins. https://en.wikipedia.org/wiki/Predictably_Irrational
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. https://doi.org/10.1037/0022-3514.67.3.366
Buehler, R., Griffin, D., & Ross, M. (2002). Inside the planning fallacy: The causes and consequences of optimistic time predictions. In T. Gilovich, D. Griffin, & D. Kahneman (Eds.), Heuristics and biases: The psychology of intuitive judgment (pp. 250–270). Cambridge University Press.
Buehler, R., Griffin, D., & Peetz, J. (2010). The planning fallacy: Cognitive, motivational, and social origins. Advances in Experimental Social Psychology, 43, 1–62. https://doi.org/10.1016/S0065-2601(10)43001-4
Flyvbjerg, B., Bruzelius, N., & Rothengatter, W. (2003). Megaprojects and risk: An anatomy of ambition. Cambridge University Press. https://en.wikipedia.org/wiki/Planning_fallacy
Kahneman, D. (2011). Thinking, fast and slow. Farrar, Straus and Giroux. https://en.wikipedia.org/wiki/Thinking,_Fast_and_Slow
Kahneman, D., & Tversky, A. (1982). Intuitive prediction: Biases and corrective procedures. In D. Kahneman, P. Slovic, & A. Tversky (Eds.), Judgment under uncertainty: Heuristics and biases (pp. 414–421). Cambridge University Press. https://doi.org/10.1017/CBO9780511809477.031
Lovallo, D., & Kahneman, D. (2003). Delusions of success: How optimism undermines executives’ decisions. Harvard Business Review, 81(7), 56–63. https://hbr.org/2003/07/delusions-of-success-how-optimism-undermines-executives-decisions
Sharot, T. (2011). The optimism bias: A tour of the irrationally positive brain. Pantheon Books. https://pmc.ncbi.nlm.nih.gov/articles/PMC3204264/
Tetlock, P. E., & Gardner, D. (2015). Superforecasting: The art and science of prediction. Crown Publishers. https://www.researchgate.net/publication/304924623_Superforecasting_The_Art_and_Science_of_Prediction_By_Philip_Tetlock_and_Dan_Gardner
