Software development has been steered by the word “requirement”, defined in dictionary as “something mandatory or obligatory”. The word carries a connotation of absolution and permanence, inhibitors to embracing change. And the word “requirement” is just plain wrong. Out of one thousand pages of “requirements”, if you deploy a system with the right 20% or 10% or even 5% you will likely realise all of the business benefit envisioned for the whole system. So what were the other 80%? Not “requirements”; they weren’t mandatory or obligatory.

Kent Beck - eXtreme Programming Explained

The essence of embracing change is making small increments and checking if they are effective, frequently.

Requirements