Baffling

I was driving down the Northway this morning and, since I drive the speed limit, I was getting passed quite a bit.  I noticed very few drivers use their turn signals.  Why?  They don't take a lot of time or effort to use and they indicate to other drivers your intentions.  Wouldn't it be safer to use them?  Are people just lazy or stupid or both?

I saw a car with Quebec plates actually use its turn signals.  I nearly had a heart attack from surprise given how rare that situation is.