Just because you're trained, doesn't mean you always remember your training.

True; OTOH, in a certain sense, complete training means you don't have to remember it; you've been trained to just automatically do it as a default maneuver.

I learned at 17 to never lock knees when standing at attention or parade rest, but to very slightly wiggle the knees, imperceptibly, as you stand there. You never stand motionless.

To this day when standing in line or whatnot, I automatically wiggle my knees to keep from locking.

Just my $.02