Driving in Italy is a competition sport.

Past the obvious "left lane is for passing only", empirical observation suggests three main rules:

Rule #1   He who drives fastest and tailgates closest, wins.

Rule #2.  No matter what lane you're in and no matter how fast you might be willing to drive, there are many, many people who want to drive considerably faster.  A significant percentage of them are located directly behind you.

Rule #3.  See rules 1 and 2.

Additional observations:  Stop signs are, at best, gentle suggestions.  And lanes are painted on the roadways for decorative purposes only.  Enormous tour buses on torturous mountain roads encounter each other head on, with far less room to pass each other than is required by the laws of physics.  Just as it is aerodynamically impossible for bees to fly but the bees don't know that, the tour bus drivers are unaware that there isn't sufficient room to pass, they just do it anyway.  

Gas is nearly $7/gallon and we've paid tolls on the highways which run into three figures.  Gotta pay for all that "social democracy" stuff somehow, I suppose.