Reason = Perceiving reality in terms of order, structure and 'what we can be sure of''.
There's a lot of use in this: To perceive reality as something orderly means the ability to interact with this order: To develop tools, farming, technology, medicine... everything to do with science.
Reality, as it is, isn't necessarily something to be used, though. It can be used - but that doesn't mean that it should be.
If we perceive reality strictly as order, we push everything unruly and disorderly to the side, and dismiss it as somehow less real than that, which we understand to be rational. Thus we create chaos - cause the disorderly aspects of existence will still be there, even if we try to set them aside and to 'see through' them.
Reason: To divide reality into order and chaos - and to assert the order over the chaos.
The order is dependent on the chaos, however - the more we seek to assert the order, the more chaos will manifest. One cannot 'win'.
If we step back, and behold reality strictly through what is - not with regards to how it can be of use - then we see that the chaos and the order are in perfect balance. That's beauty - and beauty is neither rational nor chaotic, as much as it is order sacrificing itself to the chaos, and vice versa.