Mysteries of maried life #1

I don't understand razors. The variety of choice baffles me and my bathroom is littered with stems from the two major manufacturers Gillette and Wilkinson Sword.  What annoys me most is being in thrall to the duopoly they enjoy (discounting supermarket generics as inferior) and knowing full well that they charge below minimum price for the stem and then sting you mightily for the blades.  They also have the infuriating habit of changing the stem locking mechanism to prevent the blades being interchangeable between different models.  All of this provokes both irritation and inconvenience in equal measure as I scrabble to find the right blade for the right stem first thing in the morning (never a good time for me - see previous blog).  And when  it comes to buying new blades I am frankly baffled by the range of little packets on the supermarket shelves and usually end up buying none of the above. Here is where the Mysteries of Married Life #1 comes in.  My wife does know which blade fits which stem and more often than not I have to ask her to buy them for me.  But how does she know?  How does she remember?  It's a mystery.