Our best quality, by far, is our ability to reason. Our worst would be our ability to completely and utterly ignore reason. =/
That's reason as a verb, not a noun.
Think, understand, and form judgments by a process of logic. To form conclusions, judgments, or inferances from facts or premises. The power of comprehending, inferring, or thinking especially in orderly rational ways.
With reason we understand the world closer to what it really is, not as we want it to be.