At the time that a project is conceived, there are certain expectations on how it is to be executed. This is most often the case with most startups; startups begin as mere projects. Based on the execution envisaged, people are assigned and teams are created.
I have often noticed that as the pace of things increase and changes come into play, as is often the case with startups, the teams are redistributed and resources are re-allocated. The entrepreneurs expect their teams to perform as per earlier expectations. But once such steps have been taken, it is unrealistic to expect the same standard of productivity.
The best analogy is the pit-stop in an Formula One race. 16 people are assigned to change 4 tyres in 2 seconds; if 2 people were assigned asked to do the same in 16 seconds, it probably would never happen.
The only thing that changes is 'Focus'. While executing, teams need to be focused and when teams are reassigned, some amount of focus is lost. This loss of focus hinders productivity. Hence, it is important to make sure that focus is maintained, even at the cost of hiring some more people.