Services firms grow by getting good at serving somebody, and the natural consequence is that one relationship becomes very large. It rarely feels like a risk while it is happening — the work is good, the client is happy, and turning down more of it to protect a ratio feels like an absurd reason to refuse revenue. The risk becomes visible at exactly the moment it is least manageable.
The first cost is not the obvious one. Long before any client leaves, concentration changes how you behave. You accept scope you would otherwise decline, absorb payment terms you would not agree to from anyone else, prioritise their escalations over other clients' commitments, and avoid raising problems because the relationship feels too important to strain. Each of those is a small decision and collectively they mean the firm is being run for one customer's convenience rather than its own health.
Then there is what it does to your people. A team assigned entirely to one account stops accumulating varied experience, becomes expert in a domain that has no market elsewhere, and knows perfectly well that their job depends on somebody else's budget. The best of them leave first, because they can see it. That is the second-order damage that persists even if the client never goes anywhere.
Concentration also affects what the business is worth. Any buyer or investor examining a services firm looks at revenue by client immediately, and a large single-client share reduces valuation or kills the conversation — not because the client is bad, but because the buyer is being asked to purchase a relationship they cannot control. If a sale is ever likely, this is one of the few metrics that moves the price directly.
The way out is arithmetic and slow. Concentration falls either because you lose the client, which is the bad version, or because everything else grows, which requires investing in business development at precisely the moment you are busiest and least motivated to. That means ring-fencing a portion of capacity for work that is not the large client's, and protecting it the way you would protect a product team — because the pressure to reassign it will be constant and every individual instance will be justified.
In the meantime, reduce the fragility rather than only the ratio. Multiple relationships inside the client rather than one champion who might leave. A contract with a real notice period. Documented systems so a transition is orderly rather than catastrophic. And an honest internal number: how many months could the firm operate if that revenue stopped, and what would you do in month one. Most firms have never calculated it, and calculating it is usually what finally makes the business development investment happen.
