You have that letter ... you know ...

.... the one you keep in the office drawer.  The letter that says something like, "Mr.. boss, it's been a nice run but ...."

I've had one in some form and shape now for 4 years I think.  And actually have turned in versions of it to resign from a position.   But I usually have had two other positions I was doing anyway, so it was safer.  I have another that's not so safe this time.  

and it's time.