Leap-of-Faith Assumptions

Definition

Leap-of-faith assumptions are the critical, unvalidated beliefs that every startup’s business model rests upon. They are called “leaps of faith” because acting on them requires betting the entire enterprise on beliefs that have not yet been proven true. These are not minor implementation risks — they are existential assumptions about whether the business can work at all.

Why They Must Be Tested First

Most startups fail not because they cannot execute their plan, but because they execute a plan built on false assumptions. The intuitive response to uncertainty is to plan more thoroughly — but planning around unvalidated assumptions amplifies risk rather than reducing it.

Eric Ries identifies two specific failure modes:

• The “just do it” trap: skipping planning entirely, acting on gut instinct without structured learning
• The “good old management” trap: creating elaborate plans that treat assumptions as facts, investing heavily before testing anything

The Lean Startup approach is to identify your most critical leaps of faith explicitly — then design the smallest possible test to validate or invalidate them before building further. The logic is straightforward: everything else you build depends on these assumptions being true.

The Two Critical Types

Ries identifies two leap-of-faith assumptions as foundational for every startup:

1. The Value Hypothesis: Does the product actually create value for customers? Will people use it, love it, pay for it? This tests whether the core product solves a real problem.

2. The Growth Hypothesis: How will new customers discover the product? Will the mechanism that grows the business actually work at scale? This tests whether the acquisition and retention strategy is viable.

These must be the first assumptions tested — before any other development work — because all other decisions cascade from them. A product that creates no value cannot be fixed by optimizing growth; a product that cannot grow cannot reach the customers who would value it.

Connection to Decision Theory and Cognitive Bias

Decision theory frames leaps of faith as acting under irreducible uncertainty. Research on entrepreneurial overconfidence (Camerer & Lovallo, 1999) shows that founders systematically underestimate the probability of failure and overestimate the uniqueness of their own insights. This cognitive bias makes it particularly hard for entrepreneurs to recognize their own leaps of faith — what feels like insight may be wishful thinking.

Gary Klein’s “pre-mortem” technique offers a practical counter: before committing to a plan, imagine it has already failed and work backward to identify what caused the failure. This surfaces hidden assumptions and converts them into explicit leaps of faith that can be tested.

Related Concepts

• Validated-Learning — the process by which leap-of-faith assumptions are tested
• Build-Measure-Learn-Loop — the feedback cycle that operationalizes assumption testing
• The Lean Startup - Ries - 2011 — primary source
• Value Hypothesis and Growth Hypothesis (see Value-Hypothesis, Growth-Hypothesis when created)

Future Connections

Will connect to Value-Hypothesis, Growth-Hypothesis, Genchi-Gembutsu, Minimum-Viable-Product when created.

Sources

• Ries, Eric (2011). The Lean Startup: How Today’s Entrepreneurs Use Continuous Innovation to Create Radically Successful Businesses. Crown Publishing. ISBN: 978-0-307-88791-7.

  • Chapter 5 (Leap) — primary treatment of leap-of-faith assumptions and the value/growth hypothesis distinction

• Blank, Steve (2013). “Why the Lean Start-Up Changes Everything.” Harvard Business Review, May 2013.

  • Academic framing of customer discovery as structured assumption testing; describes how traditional management planning fails in startup contexts
  • Available: https://hbr.org/2013/05/why-the-lean-start-up-changes-everything

• Camerer, Colin and Dan Lovallo (1999). “Overconfidence and Excess Entry: An Experimental Approach.” The American Economic Review, Vol. 89, No. 1, pp. 306–318.

  • Empirical research on entrepreneurial overconfidence; shows how founders systematically underestimate competition and failure risk, making it harder to recognize their own leap-of-faith assumptions
  • DOI: 10.1257/aer.89.1.306

• Klein, Gary (2007). “Performing a Project Premortem.” Harvard Business Review, September 2007.

  • Describes the pre-mortem technique for surfacing hidden assumptions before committing to a plan — a practical tool for making leaps of faith explicit and testable
  • Available: https://hbr.org/2007/09/performing-a-project-premortem

• Maurya, Ash (2012). Running Lean: Iterate from Plan A to a Plan That Works. 2nd ed. O’Reilly Media. ISBN: 978-1-449-30517-8.

  • Lean Canvas approach to explicit assumption documentation; introduces the concept of “riskiest assumption” as the first thing to test before any other development