I don't know exactly why I started to lose interest in Doctor Who. Maybe it was because, post-Christopher Eccleston, a terrific Doctor who should have stuck around for more than just a single series, the scripts and David Tennant's performance sometimes erred too much on the side of knockabout comedy.
Or maybe it was because the people behind Doctor Who, and chiefly Russell T Davies, the architect of the successful revival, seemed to start believing their own publicity and grew a little too self-absorbed for their own good.
Remember Tennant's overblown, overlong farewell episode, where the series seemed to be inviting viewers to stand back and marvel at its magnificence and cleverness?
It could be something simpler, like last year's Christmas Day special guest-starring Katherine Jenkins and Michael Gambon, which everyone else seemed to love but I thought was boring -- although it wasn't nearly as bad as one of the previous ones, featuring the Titanic in space and Kylie Minogue, looking more alien than anything else on screen.
Or perhaps it's the faintly annoying, self-contained cod-mythology that's grown up around the series, meaning you practically need a whiteboard pinned to the living room wall to keep track of all the "significant" little verbal and visual references to things that have already happened, things that have yet to happen, and things that could happen but then again might not.
Or maybe it's because the current inhabitant of the Tardis, Matt Smith, looks young enough to be my son (if I had a son), which makes watching Doctor Who feel a little like sitting on the kitchen floor playing with Dinky toys.
Whatever. I stopped watching Doctor Who some time ago, and I know many of my friends did the same.
That said, I'll be tuning in to tonight's episode, the first in the second batch of the staggered sixth series, purely out of curiosity. I mean, who could ignore an episode called Let's Kill Hitler?
Since a new season of Doctor Who is as shrouded in mystery as a CIA black ops mission, it's impossible to say how Adolf Hitler will actually figure in the episode, although given the time-travel show's reluctance to take a chance and actually alter any history, it's probably safe to predict he won't actually be killed.
While there's a strong argument for using a family-friendly series like Doctor Who as a backdoor way of encouraging younger viewers to learn about history, a storyline involving a real-life fascist dictator who tried to wipe out an entire race is a hot potato to pick up. Issues of taste are bound to be raised.
Still, it will surely be more sensitively handled than the notorious, ill-advised Heil Honey I'm Home!, a 1990 comedy commissioned by now defunct satellite channel Galaxy. Spoofing the style of 1950s American sitcoms, it featured Adolf Hitler and Eva Braun living in an apartment block, next door to a Jewish couple called the Goldensteins.
The first episode was screened just once; the other seven remain locked in a vault that not even Doctor Who's sonic screwdriver would be able to open.