The Trust Equation
Trust = (credibility + reliability + authenticity) / perception of self-interest
- Difficulty
- Easy
- Time to result
- ~ongoing to results
- Steps
- 4
- Confidence
- 88%
A diagnostic model for building trust with people who don't yet know you or your work. Trust rises with credibility, reliability, and authenticity, and falls the more people perceive you're acting out of self-interest. Breaking trust into these levers tells you exactly which one to work on when you're being met with skepticism.
Origin
Costello credits an article on First Round by her former Asana board member and now head of business, describing 'the trust equation' — the model itself originates from David Maister, Charles Green, and Robert Galford's book The Trusted Advisor.
Core principles
- 01Trust is not a single quality but a ratio of four factors.
- 02The numerator (credibility, reliability, authenticity) can be actively built; the denominator (self-interest) must be actively lowered.
- 03With a stranger, credibility is the fastest lever — and insight is how you tip it.
How to run it
- 1
Build credibility
When someone doesn't know you or your work, create credibility by bringing insight — demonstrated knowledge of the customer, market, and product that shows you know what you're talking about.
Pro tip Bringing customer insight is where you can most quickly tip the scales on credibility with someone new.
- 2
Prove reliability through your say-do ratio
Reliability is entirely about doing what you said you'd do. Track and protect your say-do ratio so people learn your commitments are dependable.
- 3
Show authenticity by being vulnerable
Be yourself and be willing to be vulnerable rather than projecting armor. Authenticity signals you're not performing a role.
Pro tip Being willing to admit something is incomplete or that you don't understand a point reads as authentic and increases trust.
- 4
Lower perception of self-interest
Make sure people know you're not in it for some other outcome or cause. High perceived self-interest divides down everything you built in the numerator.
In the wild
Costello explains that when you're met by someone who doesn't know you or your work, your job is to create credibility, and bringing the insight is where you tip the scales — then reliability via say-do ratio, authenticity via vulnerability, and managing the perception of self-interest.
→ The model gives a concrete diagnosis of which trust lever to pull with a skeptical new counterpart rather than treating trust as a vague feeling.
Common mistakes
Coming with armor instead of vulnerability
Projecting 'I know this and here's how we'll do it' lowers authenticity; people actually trust the vulnerable version of you more.
Ignoring perceived self-interest
Even high credibility and reliability get divided down if people sense you're advocating for your own agenda, so the denominator must be managed explicitly.
Is it for you?
Best for
Anyone entering a new team or role who needs to build trust quickly with people who don't yet know their work
Not ideal for
Established relationships where trust already exists and the model adds little beyond what's known
From the transcript
“she said that trust is equal to credibility plus reliability plus authenticity divided by or over perception of self-interest”
“your job is to create credibility and that's where I said like bringing the Insight is where you can really tip the scales here reliability…”
From the episode
How to ask the right questions, project confidence, and win over skeptics
Paige Costello (Asana, Intercom, Intuit)