"Over a few drinks, my friends and I compared notes on how many jobs we'd each had in the five years after leaving school or uni and it turned out to be an average of 6! Is that normal?"
For most people it used to be that, when you took a job, you thought of it as an ongoing thing that would last for as long as you felt like staying, or until your lottery numbers would come up. Today the 'job' world is an entirely different place.