The Birthday Cake Exercise for Premortems

In a recent corporate workshop, I used an exercise involving a birthday cake to teach participants how to run effective premortems rather than superficial ones.

The birthday cake exercise

I told the participants to imagine I was ordering a cake for my mother’s birthday party, then asked: “Imagine the party went badly. What could have gone wrong with the cake?”

Someone suggested: “Your mother had an allergic reaction.” That’s a perfectly plausible failure, but it also illustrates the first mistake people make when running premortems.

Mistake #1: Going deep before going broad

By immediately focusing on an allergic reaction, we had narrowed the problem space too much, too early. A better approach would have been to start with a broader risk category: my mother gets sick from eating the cake.

We could then have asked, “What are the different ways she could have gotten sick from eating the cake?” This might have yielded risks such as:

• An allergic reaction.
• Expired ingredients.
• Improper refrigeration.
• Contamination during preparation.
• Contamination during transportation or storage.

Notice how much more we could have discovered by starting with a broader category rather than immediately focusing on allergies.

It’s not that suggesting an allergic reaction was inherently wrong; it’s that jumping to narrow causes before broader ones reduces the chances of identifying all relevant risks. In theory, you can achieve both breadth and depth regardless of sequence, but in practice, once we start exploring a risk in depth, we tend to neglect breadth. So start broad, and go deep only after exhausting the broader possibilities.

Mistake #2: Jumping to solutions too early

Let’s return to the workshop. After we finished exhausting breadth by listing every possible reason my mother may dislike the cake, I asked the participants to address the risk of an allergic reaction.

Someone proposed: “Let’s order the cake from a bakery that specializes in allergy-friendly cakes.”

That sounds like a sensible solution. But because we jumped to finding solutions before understanding the different ways an allergic reaction could occur, we only mitigated part of the risk. The cake might be prepared correctly but contaminated because it was stored next to allergens in my fridge. Or someone might use a contaminated knife when serving it.

If mistake #1 was going deep before going broad, mistake #2 is jumping to solutions before going deep. Again, this restricts the problem space, resulting in a less comprehensive premortem.

The three stages of good premortems

As you may have guessed by now, good premortems have three distinct stages:

1. Exhaust all possible categories of failure.
2. Then, for each category, exhaust all possible causes.
3. Only then, address all possible causes.

Of course, not all premortems need to be fully exhaustive. Business-critical projects require longer and deeper premortems than routine projects, and for some tasks, a one- or two-minute premortem may suffice. But no matter how short the premortem is, strictly following the three stages will significantly improve its quality.

Mistake #3: Not premorteming your solutions

There’s one more step that people frequently overlook. Suppose we have decided to order the cake from a bakery specializing in allergy-friendly cakes. We might feel reassured, for we identified a risk and mitigated it.

But now let’s ask another question: “Imagine we ordered the cake from a specialized bakery, and my mother still had an allergic reaction. What could have happened?”

Perhaps the bakery prepared the cake perfectly, but someone stored it next to food containing an allergen. Or perhaps someone used the same knife to cut two different cakes, contaminating the supposedly safe one. In other words, our mitigation might have worked exactly as intended, and the failure might still have occurred.

This is why critical mitigations deserve their own premortems.

Once you’ve identified a solution, imagine implementing it successfully and still experiencing the original failure. Then ask yourself, “What might have happened?” This quick question helps uncover assumptions, overlooked causes, and weaknesses in the mitigation itself.

Use premortems!

Premortems are one of the most effective and highest bang-for-your-buck tools to ensure your projects succeed. Use them aggressively!

And if you feel like you don’t have time for them, it’s probably because you’re spending a significant chunk of your time putting out fires and correcting mistakes, and that’s likely downstream of not using premortems enough.

Further readings, by me

• A one-minute exercise to de-risk your life
• Risk management as a competitive advantage