1. Retained earnings with no job to do. A profitable shop leaves cash in the corporation because it is taxed at the small business rate on the first $500,000 of active income. That is correct — right up until the passive investment income on that cash crosses $50,000 a year and starts grinding away the small business deduction. Where the money sits matters as much as how much of it there is.
2. The owner is the company. If you are the licensed master plumber whose name is on the permits, a six-month disability does not just cost your income — it can stop the company from pulling permits at all. Business overhead expense coverage and key-person disability are cheap relative to that risk and are almost never in place when we first meet an owner.
3. Partnerships without a funded agreement. Plenty of two-owner plumbing shops have a handshake and a lawyer's template in a drawer with no insurance behind it. If one owner dies, the survivor is suddenly in business with an estate. A funded buy/sell agreement, structured properly, uses the Capital Dividend Account so the buyout money comes out of the corporation largely tax-free.
4. No plan for the exit. The Lifetime Capital Gains Exemption can shelter a substantial share-sale gain, but only if the corporation qualifies at the time of sale — which usually means purifying excess passive assets out of the operating company well before a buyer shows up. This is a two-to-three-year job, not a two-week one.