Funny thing about checklists...you gotta use 'em.

I'm very conscientious in my use of checklists. I use the ABCCCDWD
(altimeter, belts, controls, cable, canopy, divebrakes, wind, Dead (as
in "will kill you dead if you do something stupid"). I use USTALL in the
landing pattern. Undercarriage, spoilers (yeah, I know its not
consistent with D for divebrakes), trim, airspeed, lookout, land. Works
for me...usually.

Did I mention that I'm very conscientious about using my checklists?
Well, here's how I got caught out: I went through my pre-launch
checklist and got myself mentally prepared for tflight. Takeoff was as
normal. During the tow, I noticed a cockpit problem (not a flight safety
issue) that I wanted to fix before engaging in a long day of cross
country. I notified the tug that I was getting off early and landing,
and did so. Now, here's where I screwed up. I didn't go through my
checklist for the second launch. I had already done the checklist hadn't
I? As you may have already guessed, the divebrakes weren't locked and
eased themselves open during the takeoff. Having noticed that the
oncoming trees weren't dropping away as usual, I checked airspeed, found
it right on, and immediately reached for the divebrake handle which I
found full back. Closing it got us back on our normal climb.

So, use those checklists EVERY time you launch.

As an aside, my ship is a 301 Libelle, which type is known for
ineffective divebrakes. In a ship with effective brakes it would have
been more immediately obvious that the brakes were open. With the
Libelle, or other ship with weak brakes, divebrakes open on tow is a
more subtle and insidious problem, but one that could just as easily
cause the flight to end badly.