Is Reason Reasonable?

Something that I rarely hear mentioned in all things philisophical that I read and hear is the concept of the system of reason which the human mind operates on being flawed or incorrect as compared with an ultimate truth which it so often tries to reach. The reason that I myself use I view as useful because I am a pragmatic philosopher and I see all philosophy as a study of life in as far as being a human being and living a human life in a human mind and with human emotions, I seek nothing external. The idea I want to raise here is simply the question of whether reason is reasonable - our mind says that yes, one of something, and another of something, makes two of something; but if there is an ultimate truth or ultimate right it may not agree with this, our reason (it seems impoossible doesn't it) could be wrong. A single thing could have an entirely different nature than what we think it has, etc...