Knowledge is recognizing a good poker hand. Wisdom is knowing when to hold it and when to fold it.

Turn to the help wanted ads in almost any newspaper, and you'll see listing after listing asking for "three years experience ... minimum five years experience ... experienced person wanted." This holds true for blue-collar and white-collar positions alike.

The underlying mentality is hard to argue with. Most employers looking to fill a vacancy don't have the time or wherewithal to train a novice to handle the job, particularly for skilled trade positions. If you need a roofer, you can't very well take people off the street who have never installed a shingle in their lives and expect them to do so in a productive and safe manner without months if not years of at least on-the-job training.