Focussing on your Leap of Faith AssumptionsTom Green, Co-Founder @ Verticode
January 9, 2023, 3 min read

In his book The Lean Startup, Eric Ries positions Leap of Faith assumptions as the most important assumptions but, at the same time, also the riskiest assumptions. Assumptions make up a key part of the concept ideation phase of building a startup. In particular, assumptions are the core driver of the Build Measure Learn cycle which is the mechanism that allows founders to go from a basic idea to a developed functionality structure using customer feedback. In this blog, we'll explore why Leap of Faith assumptions are so important, past examples of them and how you can validate them.

Why are Leap of Faith Assumptions so Important?

When ideating a startup concept, there are always a number of assumptions that a founder will make which determine why it is a good idea. Some assumptions are big, for example "people in the USA want better access to healthy food" and some assumptions are small, such as "people in the USA have access to the internet". Leap of Faith assumptions, however, are bigger than big - they are existential. If Leap of Faith assumptions turn out to be wrong, the concept is dead in the water...

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This highlights why Leap of Faith assumptions need to be positioned at the centre of any early idea testing. The fact is, there is no point testing the peripheral features/services of your business if the core value proposition is not resonating or solving a problem for the prospective customers. In the case of a Minimum Viable Product (MVP), the Leap of Faith assumptions should be the only validation being sought after while the "extras" can wait for a later development phase.

Example of Leap of Faith Assumptions

Rent the Runway offer a great example of how to test your Leap of Faith Assumptions. They had 3 Leap of Faith Assumptions:

  1. People would Rent pre-worn clothes

  2. People would rent pre-worn clothes without trying them on

  3. People would rent pre-worn clothes without even seeing them

As you can see, each assumption gets more and more complex, or difficult. The founding team validated this by setting up clothes stalls at Prom venues in the US and seeing if they could tempt people into renting clothes on a short-term basis. In the first iteration, people were allowed to see and try on the clothes - the success validated Leap of Faith Assumption 1 (LOFA 1). In the second iteration, customers could see the clothes but not try them on - success here validated LOFA 2. And finally, the team ran a stall where customers could look at photographs of the clothing but not see it live or try it on. Success here validated LOFA 3 and gave the team the confidence to push on with the business.

How to Validate Leap of Faith Assumptions

Validating Leap of Faith assumptions can be tricky and founders have to ensure that they offer an MVP which definitively proves or disproves their assumptions. Often, this means focusing on a single feature to show that your business has demand. In the case of technology businesses, for example, it can be powerful to ensure that customers are not distracted by peripheral functionalities - remember this time of learning is not about gaining profit, it's about learning from user feedback.

If a validation test succeeds, meaning the Leap of Faith assumption was right, founders can then move on to validating less risky assumptions - while always keeping tabs on customer feedback with the product. If the validation test fails, meaning an assumption was wrong, it is time to pivot the value focus. Pivoting is a very important part of startup founding, and will be discussed further in an upcoming blog.


Leap of Faith assumptions are the most important areas for validation when starting a business. The risks of not validating your assumptions are enormous. You could end up spending tens-of-thousands on development before finding out that your customers want something different. Rather, test your assumptions first using highly targeted but low functionality products which will prove that customers want your value.

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