Key people in a construction business are easy to point out. There's only one or two in a small- or medium-sized company. And in a large company, there aren't more than three of them. A company cannot function without them.
These key people are in charge of the three main functions of a construction company: estimating and sales (getting the work), construction operations (doing the work), and administration and accounting (managing the business). A weakness in any of these areas can cause a construction business to fail. If the key person in charge of construction, estimating, or administration leaves, the company changes. The company is at risk until the replacement proves the work can still be done for a profit.