Or plain lack of money to pay more. In the life of every company there is a moment when there is not enough money to hire the next two people, but there is als

Or plain lack of money to pay more. In the life of every company there is a moment when there is not enough money to hire the next two people, but there is also a feeling that hiring those two people would take the company to the next stage so much faster as to make the hiring worthwhile. At that point you either raise more money directly from investors, or offer more equity to prospect employees, or hold back on the growth. Raising extra money takes time, so it may not fit with the timing of things. Holding back should probably be preferential to giving away equity, however somethings growth is unusually important, for example when you're in the middle of a land-grab.