12 Statements That Will Destroy Your Credibility Before Lunch
What every licensed PE needs to know before stepping into a deposition
12 Statements That Will Destroy Your Credibility Before Lunch
What every licensed PE needs to know before stepping into a deposition
Herbert Roberts, P.E. | #ForensicEngineering : inventorsmindblog.com
The Deposition Is Not the Problem. The Engineer Is.
Thirty years of building expertise. Dozens of patents, failure analyses, and design reviews. A PE stamp earned through discipline and time. And then twelve words in a deposition chair reduce it to nothing.
It happens. Not because engineers are dishonest. Because expert witness testimony operates under a legal and ethical framework that engineering school never covered — which means the engineer who walks in confident walks out excluded. I have watched it happen to colleagues with credentials that dwarfed mine. The rules are not forgiving, and opposing counsel is paid to find the gap.
What follows are 12 statements that will compromise your credibility, invite a Daubert challenge, trigger sanctions, or end 9your expert witness practice entirely. Some are obvious. Others are the kind of phrasing that feels reasonable until a federal judge explains why it is not.
The 12 Statements — and Why They End Careers
These are organized by the failure mode they represent: scope violations, methodology failures, advocacy creep, and professional boundary errors. Each one is a real pattern. Each one is avoidable.
Scope Violations — When You Go Beyond What You Were Retained to Do
1. "My opinions on this matter extend beyond my written report."
Federal Rule of Civil Procedure 26(a)(2) is not a suggestion. Every opinion you intend to offer at trial must appear in your expert report before deposition. Testimony that strays outside that written disclosure is subject to exclusion — which means opposing counsel can shut you down mid-sentence with a motion in limine. The engineer who wings it in deposition hands the other side a procedural weapon. Write the report as if the trial depends on it. It does.
2. "The plaintiff is entitled to compensation for..."
The moment you cross from engineering analysis into legal conclusion you have abandoned your role and entered opposing counsel's closing argument. The ultimate issue — who wins, what damages apply, what the legal standard requires — belongs to the court. Your job is to explain what the engineering evidence shows. The jury decides what it means legally. Any engineer who confuses these two functions will be qualified by the court as a witness who does not understand the rules of the room.
3. "I did not personally examine the component, but based on what I was told..."
Every opinion must be grounded in direct investigation. Relying on secondhand accounts, accepting the retaining attorney's narrative without examining the physical evidence, or rendering conclusions on components never inspected violates the foundational principle of forensic engineering practice. If you have not done the work, you cannot offer the opinion. There are no shortcuts in failure analysis, which is why engineers who try to take them get destroyed on cross-examination.
Methodology Failures — When the Engineering Doesn't Hold Up
4. "In my experience, this type of failure usually means..."
Experience is not methodology. Daubert and Federal Rule of Evidence 702 require that expert opinions rest on sufficient facts or data, apply reliable principles and methods, and connect that application to the specific facts of the case. "In my experience" is a signal to opposing counsel that no testable methodology exists behind the conclusion. Courts have excluded engineers with 40 years of experience for exactly this reason. Methodology must precede opinion, always.
5. "I relied on a proprietary analytical method I developed."
Novel or untested methods that have not been subjected to peer review, that lack known error rates, or that fall outside generally accepted engineering practice face Daubert's reliability prong — and rarely survive it. Published standards, recognized testing protocols, and established failure analysis frameworks are defensible. A method only you use, only you have validated, and only you can explain is an invitation to exclusion. If the methodology cannot withstand challenge, the opinion built on it will not survive either.
6. "I focused on the evidence most relevant to my conclusion."
Relevant to your conclusion is not a standard. All relevant evidence — including data that complicates, contradicts, or limits your primary finding — must be considered and disclosed. The forensic engineer who selects only the evidence that supports the desired outcome has not done engineering analysis. They have done advocacy. That distinction matters in deposition, where opposing counsel will ask directly whether you reviewed contradictory data. The answer must be yes, and you must be prepared to explain it.
Advocacy Creep — When the Engineer Becomes the Attorney
7. "What really happened here is that the company decided to save money by..."
You are not an advocate. The moment testimony crosses from objective analysis into argument for a party's position, the expert has left engineering and entered the realm of closing argument — which belongs to counsel. Your obligation is to educate the trier of fact about what the engineering evidence shows and what it means. The expert who argues the case rather than analyzing it loses credibility with judges who have seen this pattern a hundred times.
8. "The defendant clearly intended to cut corners."
State of mind, intent, and motive are outside the scope of engineering testimony. You can testify that a design choice deviated from established practice, that a lower-cost material was substituted where specification required a higher-grade alternative, or that documented maintenance schedules were not followed. What you cannot offer is why a party made a particular decision. The physical record speaks. The interpretation of why belongs to the factfinder, not the engineer.
9. "I do not believe the witness is telling the truth."
Witness credibility is exclusively the province of the jury. As an engineer you can point to physical evidence that contradicts a witness account, identify inconsistencies between testimony and documented facts, or explain why a described sequence of events is mechanically impossible. The evidence does the work. Offering personal judgments about veracity is outside your role, outside your competence, and precisely the kind of overreach that opposing counsel will use to paint you as a hired gun rather than a neutral technical expert.
Professional Boundary Errors — When Credentials Become Liabilities
10. "As a structural engineer, I can speak to the thermal failure mechanism..."
Your PE licensure defines your competency boundary, and that boundary is visible to every attorney in the room. Offering opinions outside your discipline — whether through credential creep, scope expansion under pressure, or genuine misunderstanding of where mechanical ends and civil begins — is grounds for exclusion and professional discipline. Know your lane. Acknowledge its edges. The engineer who stays within documented expertise is the one who gets retained again.
11. "My CV accurately reflects my experience in this area." (When it does not.)
Misrepresenting qualifications — whether through exaggeration, omission, or implication — is grounds for exclusion and professional discipline. Your CV must be accurate. Your licensure must be current and properly described. Your experience must be fairly represented. A PE who overstates credentials risks not only the current case but every future engagement, every licensure renewal, and the professional reputation built across a career. Opposing counsel will verify everything. Assume it.
12. "In my dual role as the company's engineer and your expert witness..."
Serving simultaneously as a fact witness and an expert witness on the same matter creates conflicts that must be disclosed and managed under the applicable rules. The roles carry different obligations, different privileges, and different standards for testimony. Blurring those boundaries without proper disclosure hands opposing counsel a procedural weapon and compromises the integrity of both roles. If you are unsure which role you occupy, that uncertainty belongs in a conversation with retaining counsel before the deposition begins, not after.
The One I Almost Said
I am going to tell you something I have never published. Early in my forensic practice, during a particularly contentious deposition, opposing counsel asked me to characterize why the design team had chosen a thinner cross-section on the failed component. I knew the engineering answer. What I almost gave was the business answer — that the pressure to reduce weight drove a decision that the failure data did not support.
That is intent testimony. That is motive. That is exactly statement #8 on this list.
I caught myself. Retaining counsel did not have to stop me. But it was close. And the reason it was close is that after three hours of technical testimony you start to feel like you own the room. You do not. The court owns the room. Your job is to explain what the evidence shows, not what you believe happened in the boardroom.
The engineer who forgets that distinction is the engineer who does not get called again.
What You Can Do Right Now
Before your next deposition, run this list. Read each statement aloud. If any of them sounds like something you might say under pressure — flag it. Discuss it with retaining counsel. Build the guardrail before you need it.
Expert witness credibility is not rebuilt after it is lost. A Daubert exclusion follows you. An adverse ruling citing methodology failure follows you. The attorney network is smaller than you think, and the reputation you protect in one case is the one that gets you retained in the next.
The 12 statements above are not academic. They are the markers of an expert witness who understands the rules of the room — and the ones who do not.
Download the Deposition Red Flag Checklist — a single-page field tool with all 12 triggers, formatted for deposition prep and leave-behind use.
This is Post 2 of 13 in The Forensic Engineer’s Field Manual. Read the full series at inventorsmindblog.com.
Herbert Roberts, PE | Licensed Professional Engineer | Six Sigma Black Belt
Forensic Engineering Consultant | 32 Years Aviation R&D | 62 Patents
inventorsmindblog.com