"But It Worked Last Time!"

Why "last time" might be completely useless information

🔥 Hook

Your friend pulls out their lucky hoodie before an exam.

"Last time I wore this, I got an A. I'm wearing it today."

Is that... logic? Kind of? It feels reasonable. There's even evidence — the A happened. And the hoodie was there.

But here's the problem: last time, you also ate breakfast, slept 7 hours, and had studied the right chapters. The hoodie was present. That doesn't mean it was relevant.

Welcome to the Argument from Precedent — and its sneaky cousin, the post hoc fallacy. Where "this worked before" becomes the entire reason to do it again — even when literally everything else has changed.

🧠 What's Actually Happening?

An Argument from Precedent uses a past success (or past practice) as the main justification for a current decision.

"We did it this way last year and it worked."

"That strategy got us to the finals in 2022."

"It's always been done like this."

The fallacy kicks in when the past example is used without checking whether the relevant conditions still apply.

Because here's what "last time" often doesn't tell you:

• Was it actually the same situation?
• What else was different?
• Did it "work" because of what you think — or for some other reason?
• Have circumstances changed?

Precedent can be useful context. It becomes a fallacy when it replaces actual analysis.

📱 Real-Life Scroll

Sports:

"Our coach's formation won us the championship in 2021. Why would we change it?"

(Because the players, opponent, league, and season are all different now.)

School:

"Last time I crammed the night before, I passed. So that's my strategy."

(Also last time: the exam was shorter, you got lucky on the topics, and you were less tired. But sure, hoodie logic.)

Business / apps:

"This marketing campaign worked in 2019. Let's do the same thing."

(Sure, if nothing in tech, social media, or consumer behavior has changed since 2019. It definitely hasn't though.)

Family:

"I raised your mom like this and she turned out fine."

(Different generation. Different world. Different kid. "Turned out fine" is doing a lot of heavy lifting there.)

Politics:

"The old policy reduced crime rates in the 90s. We should bring it back."

(Was it the policy? Or demographics? Economy? Policing methods? Lots of things were different in the 90s.)

🔍 How to Spot It

Key phrases:

• 🚩 "It worked last time"
• 🚩 "We've always done it this way"
• 🚩 "If it ain't broke, don't fix it" (sometimes valid — but often used to avoid thinking)
• 🚩 "That's just how it's done"
• 🚩 "Why change a winning formula?"

The right questions to ask:

• Is the situation actually comparable?
• What was actually different last time?
• Why did it work — do we actually know?
• Have conditions changed enough that the precedent no longer applies?

Important nuance: not all precedent is bad. Experience genuinely matters. A doctor using a treatment that has worked in similar cases is being sensible, not lazy. The fallacy is using precedent instead of analysis — not alongside it.

💬 What You Can Do

When someone invokes "last time" as the main argument:

"That's interesting — what specifically was the same, and what was different?"

This forces a real comparison instead of a vibes-based one.

Or:

"What do we actually know about why it worked? Because if conditions have changed, the result might not follow."

You're not dismissing experience. You're asking for it to be used carefully.

🎯 Your Challenge

Think of something you do "because it worked before" — a study habit, a social strategy, a way of handling conflict.

Now honestly audit it:

• When exactly did it work?
• What were the conditions then vs. now?
• Has it continued to work consistently — or are you running on one data point?

Bonus: Find one example of good use of precedent (a policy, a personal decision, a strategy) that actually does apply cleanly to the current situation. What makes it different from the fallacy version?

The past is data. But it's not destiny. 📊