Ask most SME owners how much of their revenue comes from their single biggest customer, and you'll get a rough guess, usually followed by "but we're fine, they've been with us for years." That's precisely the sentence owners said about the customer who left.

US accounting standards (ASC 280-10-50-42) require public companies to separately disclose any customer that makes up 10% or more of revenue — not because 10% is inherently dangerous, but because regulators decided that's the threshold worth telling investors about. SME owners rarely have to disclose anything to anyone, which is exactly why customer concentration quietly becomes someone else's problem to notice — usually a bank, a buyer, or an owner's own cash flow, at the worst possible moment.

Run it once and it's uncomfortable in a way no survey needs to prove. A business with four roughly equal customers loses 25% of revenue the day one leaves. A business with one customer at 40% of revenue loses almost half overnight — not because the market turned, not because the team underperformed, but because one phone call happened. That's not pessimism. It's arithmetic every SME owner is running without realising it, every day they don't check the number.

"I have grown my business 5x since working with Kevin. Everything Kevin told me to do was the complete opposite of what I had been doing. Working with Kevin has truly been a complete game changer."

— Richard, Chem Suppliers

The biggest customer is usually also the easiest revenue — the one that doesn't need chasing, the one where the relationship already exists. Deliberately spending time and money on smaller, harder customers to dilute dependence on the easy one feels like working against your own instincts. It is, which is exactly why most owners need someone outside the relationship to make the case for diversifying before the easy customer makes the decision for them.

If you can't say your top customer's share of revenue to the nearest 5% right now, that's the first number we find together.