Business is rational at the micro or transactional level; and irrational at the macro or strategic level.
The individual decisions at the transactional level are binary in nature. Something is sold or not. A decision is made and the answer is either yes or no. As isolated elements, individual decisions are easy to work with in an organization.
As one considers the transactions in aggregate, the situation becomes more complicated as patterns begin to appear in the data. Many more factors must be taken into account to gain a deeper understanding of the information.
At times, the root causes of problems may be concealed by other issues. For example, a business's sales may be strong, but the culture or morale of the company is inhibiting future growth. In this case, managers reacting to the hard data would mis-diagnose a problem if they didn't study all aspects of the organization. Design is a tool that can help a leader naturally see the big picture and determine how to create effective change.
The challenge for organizations is resisting the urge to apply rational thought to solving irrational problems. Solutions that may work at the micro level of an organization do not readily translate into addressing more complicated systemic problems at the macro level.