I have been blessed with mentors that have extolled the virtues of "common sense."  Shortly after a lab mishap when I worked at Lawrence Berkeley National Laboratory, my supervisor was excitedly instructing a graduate student in what he should have done.  When the message was not getting through, the supervisor threw up his hands in exasperation and said "I expect you to use common sense, but remember, my sense is the most common of all."

Using common sense is one of those skills, like intuition, that can be developed with observation and training.  What constitutes "common sense" becomes more obvious as one becomes more mature and experienced.  However, many people fail to develop this sense over time because they have never adequately recorded their experiences.

When I teach project management, I recommend that practioners develop the habit of recording the results of their decisions in a "learning journal".  A "learning journal" can be as simple as a cheap, small spiral notebook or as elaborate as a section in your daily planning system.  In most cases, a manager is never going to have enough information to form a perfect decision.  However, that same manager can record the decision, the circumstances and the outcome.  This is a small part of the project manager's own "Lessons Learned" documentation.  Over time, the individual learns to understand when decisions are made from gut intuition and the application of common sense.  This increases comfort in the process and encodes such common sense into the manager's genes.

Verse 57* of the Tao touches on the ability to be comfortable in decision making both in the presence and absence of intuition and common sense.

"To rule the state, have a known plan
To win a battle, have an unknown plan
To rule the universe, have no plan at all"

*Tao Te Ching, The Definitive Edition, Lao Tzu with Translation and Commentary by Jonathan Star, Jeremy P Tarcher/Penguin, 2001, page 70