You have a short hair growth cycle

We wish we could say that hair has the potential to grow infinitely, but that’s not quite true. On the contrary, the hair has a “pre-programmed” cycle, called the hair growth cycle. The hair cycle has 3 phases: the anagen phase, where the hair actually grows; the catagen phase, a transition phase where the hair follicle shrinks and hair growth starts to slow down; and the telogen phase, where the hair is just sort of sitting on your head–not quite growing, but not quite falling out either. Eventually, it will fall out, and a new hair will begin to grow in its place.

These phases have pre-defined durations. The anagen phase, when the hair is actively growing, can last anywhere between two and six years, and will define the period of time during which your hair will continue to grow. Towards the end of this period, the hair shaft will stop growing–and then, yes, you will notice that you can’t get beyond a certain length. So, in practice, your hair isn’t born destined to a maximum of 30cm of growth; but it may be born destined to a maximum of 4 years of growth (for example).