In my experience, here are a few common mistakes made by both liberals and conservatives.

An easy liberal mistake: Never checking one’s own ideas against the wisdom of tradition; and often wanting to impose those ideas on the rest of us (usually through higher taxes and the increase of government programs).   Don’t schools always need more money?  Aren’t some people always in need of medical care?   There is a difference between doing something because it makes you feel good (acting in service to your own desires) and doing something out of a sense of moral duty, which you may not desire (helping a guy out of burning car, at great risk to yourself, this is a Kantian analysis).   Just because you are compassionate does not mean that you are wise. 

An easy conservative mistake:  Thinking that there is a moral code, and wanting to impose it on the rest of us.  The conservative mistakes his own ideas for transcendent ideas.  The Ten Commandments, an oath of honor…etc will always fail in light of life’s complexities.   Such ideas can be good guides, but not absolutes.  Individual liberty is under great threat from such arguments.  

Does this make me a centrist?  a libertarian?