Why Adding More Evidence Makes Your Point Weaker
You think five examples prove your case better than two. You’re wrong. Every weak receipt you add lowers the average strength of your argument, and your audience stops trusting the strong ones. By the end, you’ll know how to audit your evidence, cut what dilutes your claim, and present only what raises the floor.
The Dilution Effect (Why More Evidence ≠ More Persuasion)
Your brain doesn’t add up the strength of each piece of evidence. It averages them. In a study of 3,059 Americans, researchers found that participants who saw a drug’s complete list of side effects—both major and minor—rated the overall severity significantly lower than those who only saw the major side effects. More information made the risk seem smaller, even though the actual risk was identical.
When you present three strong arguments and two weak ones, your audience doesn’t think “this person has five reasons.” They think “the average quality here is mediocre.” The weak arguments don’t disappear—they drag down the strong ones. This is the dilution effect. Your brain processes diagnostic information (relevant to the judgment) and non-diagnostic information (irrelevant or weak) together, then averages them into a single impression.
The fix isn’t subtle. You don’t need to polish the weak arguments. You need to delete them. Every sentence in your case should raise the floor of your argument, not lower the ceiling.
Strong vs Weak Receipts (The Quality Hierarchy)
Not all evidence is created equal. Strong receipts are primary sources, verifiable data, and examples where cause and effect are clear. Weak receipts are anecdotes, secondary sources, and claims you can’t verify in under two minutes.
Strong: “A 2025 study in Nature Human Behaviour found that personalized AI arguments increased persuasion by 81.2% (odds ratio) in online debates.” You can fact-check this. The institution is named. The year is recent. The finding is specific.
Weak: “Studies show that personalization works.” Which studies? When? What did they measure? You’ve given your audience nothing to verify, which means they can’t trust it. And if they can’t trust one piece of your evidence, they start questioning all of it.
The quality hierarchy: original research > named secondary sources > unnamed sources > anecdotes > your opinion. If you’re building a case and everything below the second tier can be cut, cut it. The audience will believe two verifiable claims over five unverifiable ones every time.
The Cut Test (If You Can’t Explain Why It’s Here in 10 Words, Delete It)
Open your last argument—email, presentation, essay. Highlight every piece of evidence. For each one, answer this question in 10 words or less: “Why is this evidence necessary to prove the claim?”
If you can’t answer, the evidence is decorative. It’s there because you thought “more is better” or because you spent time finding it and don’t want to waste the effort. Delete it anyway. Research on legal arguments shows that the brain doesn’t distinguish relevant from non-relevant information when averaging—irrelevant information dilutes persuasive power.
Example: You’re arguing your team should adopt a new tool. You list five benefits: faster workflow, lower cost, better integrations, popular with other teams, easy to learn. The last two are weak. “Popular with other teams” is social proof, not evidence of value. “Easy to learn” is subjective. Cut them. Now you have three verifiable claims that each carry weight.
Practical step: After drafting your next argument, run this filter. For every piece of evidence, ask: “Does removing this make my case weaker?” If the answer is no, it’s not evidence—it’s filler. Remove it before you hit send.
Building Arguments That Get Stronger With Every Line
The best arguments follow a pattern: claim first, strongest receipt second, second-strongest receipt third, transfer last. You front-load the power. By the time the audience reaches your conclusion, they’ve already been persuaded.
Every line should either support the claim directly or connect the evidence to application. If a sentence does neither, it’s weakening your case. This applies to written arguments, verbal pitches, and presentations. The structure is the same: open with the claim, follow with only your best receipts, end with what the audience does next.
Test this on any persuasive text. Pull up a pitch deck or a successful op-ed. Count the pieces of evidence. You’ll rarely see more than three. The writer knew that four mediocre points lose to two strong ones. They cut everything that didn’t raise the floor.
Transfer: Before your next presentation, list all your evidence. Rank each piece from strongest to weakest. Keep the top three. Delete the rest. Present those three in descending order of strength. Watch how much faster your argument lands when you’re not asking the audience to average weak points with strong ones.