Knowing

The biggest impediment to learning is knowing.

When you already know everything there is to know about a subject, you close yourself off from discovering (or re-discovering, or uncovering) new things. Why should you be open to that stuff? You already know it!

This hurts us everywhere in our lives. Think about the damage caused when you know everything about your spouse? If there's nothing to learn, then you need to find a new challenge. I'm not saying its the only reason that people cheat, but I'm sure it plays its non-trivial part.

Learn more. Know less.