There is a point where every additional person makes a project slower, not faster. Communication overhead grows with the square of the team; output grows at best linearly.
Small teams avoid the tax. Three people can hold the whole system in their heads and decide in minutes what thirty schedule a meeting to discuss.
Speed is not just nice. In early markets it is often the only durable advantage.
The Coordination Tax
Every handoff and status update is a cost the small team does not pay.
The lesson is to stay small far longer than feels comfortable.