Scalability

Software scales: the ten-thousandth user costs almost nothing. Consulting does not: the tenth client needs the same hours as the first. Neither is better, but they cap out in completely different places.

Scalability is the main reason two businesses with identical revenue today can be worth wildly different amounts in five years.

Most businesses sit between the two extremes, and the useful question is where the next constraint appears. A productised service scales until the founder's review time runs out. An agency scales until hiring quality falls. A course scales until the market is saturated. Name the constraint you will hit first and you have named your ceiling, which is more useful than the label.

Scale changes what breaks, not only what earns. Support volume, refunds, fraud and infrastructure all grow with users while the price does not, which is why gross margin tends to fall as a product scales unless somebody is deliberately defending it. Plan for the second thousand customers costing more to serve than the first hundred, not less.