An ICP is a decision tool, not a description
Most written ICPs are demographic sketches that never change a decision. A useful one answers four operational questions: who to target, why now, who to refuse, and where to reach them. If a document cannot settle an argument about whether to take a particular deal, it is not doing its job.
The disqualifiers do the work
The most valuable section is the one most teams skip. Early-stage companies lose more time to badly-fit customers than to missed ones — a customer outside the profile consumes support, distorts the roadmap, and churns anyway. Three explicit disqualifiers save more than any amount of targeting refinement.
Trigger events beat firmographics
Knowing that you sell to 10–50 person SaaS companies tells you who. It does not tell you when, and timing is most of outbound. A company that just raised, just lost a growth hire, or just got asked for a distribution plan by its board is the same firmographic profile in a completely different state of urgency.
One ICP at a time
The most common failure is defining three segments before one is proven. Each additional segment divides messaging, channel focus and product attention. Prove one, then expand deliberately.
Questions
How do I know if my ICP is right?
Look at retention by segment. The group that retains best is your real ICP, whatever your document says. If your best-retaining customers do not match the profile, believe the data.
Should the buyer and the user be the same person?
Often at seed stage, rarely upmarket. When they diverge you need two messages — one about outcome for the buyer, one about daily experience for the user — and a plan for how the user builds the internal case.
How specific is too specific?
If fewer than a few hundred companies match, you have a target account list rather than an ICP. That is fine for outbound, but it will not support a marketing channel.
How often should this change?
Review quarterly. It should change as your customer base teaches you who actually gets value — but not so often that nobody can remember what it says.